What seems to never be discussed on this topic is that Canadians mortgages in arrears are less than 0.35% while American mortgages in arrears are over 10 times greater. Doesn't that factor alone put banks operating(even Canadian ones) in America at a greater disadvantage than a homebody like CIBC? Yet it is CIBC that is discounted because it hasn't a large footprint in the US. 
I think the mistake a lot of the earlier American short sellers of Canadian financials made was thinking there was going to be a housing crises based on coming interest rate increases where they should have used mortgage defaults as a guide line. It sure hasn't happened here yet.