We crossed and immediately went to a bank and got $300 in Canadian. It just makes sense that if you go to a foreign country to use their currency. If Canadians come to the U.S. they'll find not all businesses would accept their Canadian dollars. We stayed in the Provincial Parks and most had fee boxes to put your 'Canadian' $ into an envelope with no host available and cash only. Also, laundries require Canadian and the shopping carts at the groceries...so having Canadian cash is desireable. Also check into getting a different credit card that doesn't have an exchange fee. We used a debit card that had no fee. Upon our return 3m later we had about $30 left. We crossed and tried to exchange it for U.S. near Glacier Nat'l Park. No can do. We just donated it to the Nat'l Park in their donation box. Although that's a worthy cause, if you really want none left over and are nearing the border, buy something with it...fuel, restaurant, etc. to use it up.