You pay the regular GST and PST. If you send via UPS from the USA to Canada, they will rape you with brokerage fees that range from 25% to 100% of the value of what you are receiving. Use FEDEX or USPS... never use UPS!!
I just got a camera body, lens & memory card from B&H, paid $47 for the shipping (UPS) and then $54 in brokerage & tax (I tink it was PST, but I could be wrong). I think the duty was only $10-12. Fedex may end up cheaper in the end despite the initially higher shipping fee. B&H is AMAZING :hail:, I messed up and ordered the wrong lens, and they let me exchange it straight away with no hassle.
Even with the shipping and brokerage fees, I still saved over $250 by buying from them.