Well, according to
this article you will have to pay GST and PST (not in Alberta). Here is the
web site for the governement agency that can really answer your question.
I would only look to this route if there was a piece of equipment I couldn't find here or if the piece was massively cheaper. By the time shipping, taxes, duty and fees get tacked on it can eat up a lot of savings.
Another consideration is warranty. Not everything has international warranties (actually pretty rare) and you may find that you would have to ship the piece back to the U.S. in case of a problem.
I'm not saying that buying from the U.S. is a bad idea but consider it carefully. I guess something used off Ebay is a different story.
Check with Canada Customs for exact duty rates.
I've ordered hard to find DVDs frm the U.S. and paid no duty or taxes. They just show up in the mail box.