Calomiris and Haber ("Fragile By Design") have run the natural experiment between the U.S. and Canada over the 2008 bubble period. The conclusion is the opposite of yours - Canada really just has the one bank, and sailed right through the crisis because they didn't hold as many rotten mortgages.
And in a way, the big banks are effectively nationalized in the U.S. We do maintain parallel governance structures because fully nationalized banks ( like the Bank of England in Britain's Mercantilist heyday ) are ... well, mercantilist.
Is this supposed to be a figure of speech suggesting Canadian banks policies are so similar they are essentially the same bank? The three largest of the Big Five (RBC, TD and Scotia) are so similar in size none of them can even be said to lead the market.
And in a way, the big banks are effectively nationalized in the U.S. We do maintain parallel governance structures because fully nationalized banks ( like the Bank of England in Britain's Mercantilist heyday ) are ... well, mercantilist.