Filed by Bank of Montreal
Pursuant to Rule 425 under the Securities Act of 1933
and deemed filed pursuant to Rule 14a-12 under the
Securities Exchange Act of 1934
Subject Company: Marshall & Ilsley Corporation
SEC Registration Statement No.: 333-172012

This filing, which includes a February 3, 2011 letter to clients of M&I Institutional Trust Services, may contain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 and comparable “safe harbour” provisions of applicable Canadian legislation, including, but not limited to, statements relating to anticipated financial and operating results, the companies’ plans, objectives, expectations and intentions, cost savings and other statements, including words such as “anticipate,” “believe,” “plan,” “estimate,” “expect,” “intend,” “will,” “should,” “may,” and other similar expressions. Such statements are based upon the current beliefs and expectations of our management and involve a number of significant risks and uncertainties. Actual results may differ materially from the results anticipated in these forward-looking statements. Such factors include, but are not limited to: the possibility that the proposed transaction does not close when expected or at all because required regulatory, shareholder or other approvals and other conditions to closing are not received or satisfied on a timely basis or at all; the terms of the proposed transaction may need to be modified to satisfy such approvals or conditions; the anticipated benefits from the proposed transaction such as it being accretive to earnings, expanding our North American presence and synergies are not realized in the time frame anticipated or at all as a result of changes in general economic and market conditions, interest and exchange rates, monetary policy, laws and regulations (including changes to capital requirements) and their enforcement, and the degree of competition in the geographic and business areas in which M&I operates; the ability to promptly and effectively integrate the businesses of M&I and BMO; reputational risks and the reaction of M&I’s customers to the transaction; diversion of management time on merger-related issues; increased exposure to exchange rate fluctuations; and those other factors set out on pages 29, 30, 61 and 62 of BMO’s 2010 Annual Report. A significant amount of M&I’s business involves making loans or otherwise committing resources to specific companies, industries or geographic areas. Unforeseen events affecting such borrowers, industries or geographic areas could have a material adverse effect on the performance of our integrated U.S. operations.

Additional factors that could cause BMO Financial Group’s and Marshall & Ilsley Corporation’s results to differ materially from those described in the forward-looking statements can be found in the 2010 Annual Report on Form 40-F for BMO Financial Group and the 2009 Annual Report on Form 10-K of Marshall & Ilsley Corporation filed with the Securities and Exchange Commission and available at the Securities and Exchange Commission’s Internet site (http://www.sec.gov).

In connection with the proposed merger transaction, BMO has filed with the Securities and Exchange Commission a Registration Statement on Form F-4 that includes a preliminary Proxy Statement of M&I, and a preliminary Prospectus of Bank of Montreal, as well as other relevant documents concerning the proposed transaction. Shareholders are urged to read the Registration Statement and the preliminary Proxy Statement/Prospectus regarding the merger, the definitive Proxy Statement/Prospectus when it becomes available and any

other relevant documents filed with the SEC, as well as any amendments or supplements to those documents, because they will contain important information. A free copy of the preliminary Proxy Statement/Prospectus, as well as other filings containing information about BMO and M&I, may be obtained at the SEC’s Internet site (http://www.sec.gov). You can also obtain these documents, free of charge, from BMO at www.BMO.com under the tab “About BMO — Investor Relations” and then under the heading “Frequently Accessed Documents”, from BMO Investor Relations, Senior Vice-President at (416) 867-6656, from M&I by accessing M&I’s website at www.MICorp.com under the tab “Investor Relations” and then under the heading “SEC Filings”, or from M&I at (414) 765-7814.

BMO and M&I and certain of their directors and executive officers may be deemed to be participants in the solicitation of proxies from the shareholders of M&I in connection with the proposed merger. Information about the directors and executive officers of BMO is set forth in the proxy statement for BMO’s 2010 annual meeting of shareholders, as filed with the SEC on Form 6-K on February 26, 2010. Information about the directors and executive officers of M&I is set forth in the proxy statement for M&I’s 2010 annual meeting of shareholders, as filed with the SEC on a Schedule 14A on March 12, 2010. Additional information regarding the interests of those participants and other persons who may be deemed participants in the transaction may be obtained by reading the above-referenced preliminary Proxy Statement/Prospectus and the definitive Proxy Statement/Prospectus when it becomes available. Free copies of this document may be obtained as described in the preceding paragraph.

		Gilles G. Ouellette President & CEO Deputy Chairman, BMO Nesbitt Burns		Private Client Group 1 First Canadian Place, 49th Floor P.O. Box 150 Toronto, ON M5X 1H3 Tel.: 416-359-4176 Fax: 416-359-4991 gilles.ouellette@bmonb.com

February 3, 2011

Dear Clients and Friends of M&I Institutional Trust Services,

As you may know, BMO Financial Group (BMO) recently announced a definitive agreement under which BMO will acquire Marshall & Ilsley Corporation (M&I). The transaction is subject to customary closing conditions, including regulatory approvals and approval from shareholders of M&I. We anticipate the closing will occur prior to July 31, 2011.

Established in 1817 and based in Toronto, BMO Financial Group serves more than 10 million personal, corporate and institutional customers in North America and internationally. Our United States operations are headquartered in Chicago with affiliated locations in 12 states. Harris Bank, part of the BMO family for 26 years, has a significant presence in the U.S. with 321 offices in Illinois, Indiana, and Wisconsin.

As a valued client of M&I Institutional Trust Services (ITS), we wanted to share with you our excitement about the acquisition and the capabilities M&I’s nationally-recognized institutional trust business brings to the new partnership.

We stand committed to investing in this business and maintaining the same high level of service you currently receive from the ITS management team, your relationship manager and support teams. We are also committed to continuing to invest in the communities in which they serve.

If you have any additional questions, we welcome the opportunity to talk with you.

Sincerely,

/s/ Gilles Ouellette

Gilles Ouellette
Global Head, BMO Wealth Management

Additional information for shareholders

In connection with the proposed merger transaction, BMO has filed with the Securities and Exchange Commission a Registration Statement on Form F-4 that includes a preliminary Proxy Statement of M&I, and a preliminary Prospectus of Bank of Montreal, as well as other relevant documents concerning the proposed transaction. Shareholders are urged to read the Registration Statement and the preliminary Proxy Statement/Prospectus regarding the merger, the definitive Proxy Statement/Prospectus when it becomes available and any other relevant documents filed with the SEC, as well as any amendments or supplements to those documents, because they will contain important information. A free copy of the preliminary Proxy Statement/Prospectus, as well as other filings containing information about BMO and M&I, may be obtained at the SEC’s Internet site (http://www.sec.gov). You can also obtain these documents, free of charge, from BMO at www.BMO.com under the tab “About BMO — Investor Relations” and then under the heading “Frequently Accessed Documents”, from BMO Investor Relations at investor.relations@bmo.com or 416-867-6642, from M&I by accessing M&I’s website at www.MICorp.com under the tab “Investor Relations” and then under the heading “SEC Filings”, or from M&I at (414) 765-7814.

BMO and M&I and certain of their directors and executive officers may be deemed to be participants in the solicitation of proxies from the shareholders of M&I in connection with the proposed merger. Information about the directors and executive officers of BMO is set forth in the proxy statement for BMO’s 2010 annual meeting of shareholders, as filed with the SEC on Form 6-K on February 26, 2010. Information about the directors and executive officers of M&I is set forth in the proxy statement for M&I’s 2010 annual meeting of shareholders, as filed with the SEC on a Schedule 14A on March 12, 2010. Additional information regarding the interests of those participants and other persons who may be deemed participants in the transaction may be obtained by reading the above-referenced preliminary Proxy Statement/Prospectus and the definitive Proxy Statement/Prospectus when it becomes available. Free copies of this document may be obtained as described in the preceding paragraph.