TORONTO – The Bank of Montreal is buying a Milwaukee-based bank, the latest example of Canadian banks snapping up U.S. financial institutions battered by the financial crisis.

Canada’s fourth-largest bank announced Friday that it was acquiring Marshall & Ilsley Corp. for $4.1 billion in stock, doubling its presence in the U.S. from 321 branches to 695.

The news sent shares of M&I surging 18 percent, up $1.06, to $6.85, while U.S.-traded shares of the Bank of Montreal fell $4.40, or 7.1 percent, to $57.26.

Canadian banks, ranked the soundest in the world by the World Economic Forum, weathered the economic crisis far better than their counterparts in other countries. In a banking system dominated by five major players, Canadian banks have been looking across the border to find growth opportunities, casting an eye toward distressed U.S. banks.