Here are a couple of comments...
First of all, Canadian banks have been acquiring US banks for years. Commerce Bancorp just happens to be one of the larger purchases. You can count the number of Canadian banks on one hand, so growth for any of them in Canada is limited. Hence, they acquire banks in other countries.
The "economic problems" connection is indirect. I suspect that the appreciation of the Canadian dollar is the more direct cause. Any company in the US is now almost 20% cheaper for Canadians to buy now than a year ago.
I occasionally comment on issues like this in my weekly commentary at...
http://TSX.ProfiTrend.com
You might want to go back through some of the archives.