You should always search for the best deal for your money. For e.g. I prefer to buy books from Amazon, but I always check Abebooks where sometime you find the international edition of the same book at 20% the price from Amazon (this doesn't really work for literature, but for Math or Programming books you have a good chance to find a better deal).
As a side note, you should probably check Amazon.ca where you have free shipment for Canada for order over $25.