Surprisingly enough if you just PM the person, explain to them that it doesn't cost that much more to ship to Canada and you'll cover all expenses and that you understand that whatever happens at customs is out of their control they're usually more than willing to ship to Canada.
If there's something you really want, it never hurts to try. It's only happened to me once that someone was adamant about not wanting to ship to Canada.
I do have to say though that I did get a great sense of satisfaction when I was selling something and labeled it as "Canada" only and had a whole bunch of PMs from Americans asking if I'd consider shipping to the US