Buyer should pay for shipping. Do not insure USPS to Canada- the coverage stops at the border (I live in Canada, and have been bitten by this). Send expensive items by Purolater, etc.
Instead of insurance send it airmail to Canada; fast and safe. Registry covers all the way, but expensive for lower cost items.

I buy books from Europe and Australia; always sent air. Check the rates and you will see that air in many cases is little more than surface.