In many cases, in the U.S. or even here in Canada, you're not dealing with the bank directly; you're dealing through a payment processor. These are the people who actually process your payments, even though the credit card companies—say VISA or MasterCard or the banks—sometimes get the heat. In a way, it's the payment processors as well that are part of the issue, so on the banks' side, their portion is now restricted through the Durbin Amendment or others. In the U.S., at least, they are now going to have to be consistent because of that amendment. That only applies to debit cards, of course.
In Canada it's different, because really there is not much competition, and it's more that you negotiate one on one, so the fees vary by merchant.