When you make a purchase through Priceline and change your currency to CAD, so that the summary of charges shows:
Will your credit card be charged that exact amount in Canadian funds? Or is that just an estimate and Priceline will still charge in USD to be converted by your credit card?
My experience is that when the price is in C$, that is what you are charged. Priceline doesn't have C$ pricing for everything but when it does it's not like eBay that gives a US $ price. Usually if there is a conversion, the US price is shown with the estimated conversion.