I have sold alot of parts to Americans, and I mostly use Canada Post to ship, except the bigger items, which go UPS. Canada Post's courier service is cheaper, and the buyer doesn't get hit with the brokerage fees. You can estimate shipping costs for Canada Post here:
http://www.canadapost.ca/personal/rates/default-e.asp
And UPS here:
http://www.ups.com/content/ca/en/index.jsx
As for payment, I would suggest setting up a PayPal account for electronic transfer, or insist on US Postal Internatinal money orders to avoid being ripped off. I learned the hard way about this. Do not accept personal cheques from anyone!
BTW, Canada Post also offers a package tracking feature, which most people like.