It is a matter of regulation. Canada's banks are far less volatile then the american banks since they did not get caught up in the subprime mortgage securities fiasco. The regulatory agency for Canada found it too risky and so they did not buy into it.ie: less moral hazard. But the down side is that it is harder to start small companies in Canada because of the same regulatory measures. I do think though that Canadian banks are becoming the new Swiss banks because of their stability.
Not sure how Canadian banks are regulated but the nail in the coffin for US banks was when the Glass/Steagal act was repealed and banks were allowed to become brokerage houses, mortgage companies and speculators.