What do I need to know about shipping to Canada?

[yellowperil]

Someone won one of my eBay auctions for a heavy item (speaker set). I had listed that the auction was open for the continental U.S. only, but he seems to be willing to pay the extra shipping (and I'm not too keen on going through the hassle of relisting, getting fees refunded, etc.). What do I need to know about customs, extra fees, etc.? Thanks.