The obvious reason that CIBC"s stock price is stunted compared to to others of the big five is based on its past poor performance during the great recession. They purchased 10 billion in subprime mortgages      at exactly the wrong time that I think went to zero in short order. The level of trust has not yet returned.
 What I find interesting is that the most Canadian bank CIBC makes the highest return due to the big five  monopoly in in this country, while the most American bank TD has returns similar to the lower profits found south of the border.
 I'm sure a case could be made not to expand into the States unless you can get a great asset at a good price.