I usually just use Canadian ATMs to take out cash if needed (taking the hit for the ATM fees, but the exchange rate is fair), but these days there are a number of credit cards that don't charge foreign transaction fees and have similar rates. Just know that you'll be "The American" when you whip out your card for the mobile terminal and they need to swipe it and print out a receipt because the US is chip and signature while most of the rest of the world is chip and PIN.