Toronto Montréal Calgary Ottawa Vancouver New York | | March 26, 2019 Bank of Montreal 1 First Canadian Place 18th Floor Toronto, ON M5X 1A1 Dear Sirs/Mesdames: Bank of Montreal – US$1,750,000,000 2.900% Senior Notes due 2022 and US$500,000,000 Floating Rate Notes due 2022 We have acted as Canadian counsel to Bank of Montreal (the “Bank”) in connection with the issue and sale today (the “Offering”) by the Bank of US$1,750,000,000 aggregate principal amount of the Bank’s 2.900% Senior Notes due 2022 (the “Fixed Rate Notes”) and US$500,000,000 aggregate principal amount of the Bank’s Floating Rate Notes due 2022 (the “Floating Rate Notes”, and together with the Fixed Rate Notes, the “Notes”), constituting part of the Senior Medium-Term Notes, Series E of the Bank, pursuant to the distribution agreement dated September 23, 2018 (the “Distribution Agreement”) between the Bank and BMO Capital Markets Corp., the terms agreement dated March 21, 2019 (the “Terms Agreement”) between the Bank and BMO Capital Markets Corp., BNP Paribas Securities Corp., Goldman Sachs & Co. LLC, J.P. Morgan Securities LLC and Wells Fargo Securities, LLC, as representatives of the agents named therein, and the senior indenture dated as of January 25, 2010, as it may be amended and supplemented from time to time, including as supplemented by the First Supplemental Indenture thereto dated September 23, 2018 (collectively, the “Indenture”), between the Bank and Wells Fargo Bank, National Association, as trustee. Capitalized terms used herein and not otherwise defined herein have the meanings ascribed to such terms in the Terms Agreement. We have examined copies, certified or otherwise authenticated to our satisfaction, of the following: (i) the Distribution Agreement; (ii) the Terms Agreement; (iii) the Indenture; (iv) the registration statement of the Bank on FormF-3 dated April 4, 2017 and Amendment No. 1 thereto dated April 27, 2017 (collectively, the “Registration Statement”); and |