I'm from canada... other then the points mentioned always tell your buyers that it is THEIR responsibilty for duty and brokerage charges, sometimes you get hit with that, and its just part of crossing the border.
I usualy do all my sales in US, paypal does currency exchanges, so a CDN can send us funds and i can take american funds and then swap them into CDN if i want, not a large issue, another note is customs can hold the package and shiping times may be affected as long as both parties are understanding of this its not a big issue!
Ry