When buying things in the US from Canada, there are often different options to pay: PayPal, credit cards, etc.
In my case, I am (too) often paying for my voip.ms line (DID and usage).
Despite being a Canadian company, they only charge in USD, probably because they need to pay their providers in USD, and don’t want to lose money when the exchange rate is abysmal (1.40 CAD = 1 USD right now!)
When paying an invoice in USD from Canada, not all payments methods are equals. Some will charge more to convert currency. PayPal in particular is pretty bad.
My test: paying 25 USD + taxes (28.74 USD) using PayPal, a MasterCard from MBNA (Smart Cash Platinum Plus), and the VISA from Amazon.
PayPal: 41.23 CAD
MasterCard MBNA: 41.10 CAD
VISA Amazon: 40.15 CAD
So if you often buy in USD from Canada, getting the VISA from Amazon might not be a bad idea. You’ll save (a lot) in the long-term.