Booking AC through the U.S. site or the Canadian site yield slightly different prices based on which conversion rate they're using at the time. It's typically on a couple of dollars different, but there can be substantial differences if foreign exchange is particularly volatile. I generally use the U.S site primarily because it's far more advantageous to use my U.S. credit card and I don't have to worry about arbitrage in the case of a cancellation or refund.