I live in Canada. We call the 49th parallel the $49 parallel as no envelope shall pass for less money. I will buy a $9 item off of ebay and easily have a $28.00 shipping bill if I am not careful. It all comes down to the experience of the shipper.
I concur the cheapest solution is to have the US item shipped to a US address - lots of border companies that receive and hold goods for Canadians.
Importing to Canada is not a big deal. You fill out a 3x4 green form at USPS that says who the sender is, and who the receiver is. A description of whats in the box (about 2" of the form is dedicated to this so you don't need to (or get to) be too verbose. You then check off that the goods are not illegal, and you check off that the goods are not hazerdous or flamable. Finally a estimated value of the goods.
If you ship via Fedex or UPS they send the parcel to a Customs broker - who fills in the same form. Charges a min fee of $35 and if the goods are over a certain $$ you then pay a percentage of the value of the goods on top of that. Then there are shipping fees, oversize fees, etc etc etc. Its a scam. You can hire your own custom broker but unless you do a lot of shipping and receiving its not going to be worth it.
If you find a shipper and there are lots of companies that will ship goods on the back of a truck (reality show shipping wars) you create a document called a proformia invoice. The trucker gets to the border, the customs guys goes through his shipping ledger which includes your proformia invoice. This is in replacement of the 3x4 USPS form.
A Proformia Invoice is nothing special - You just write on a piece of paper "Proformia Invoice" , lists the contents of box, country of orgin (where its made), serial number, model number etc and a value. Of course the From and To address as well. I suggest printing at least 4 copies of this and taping to each side of the box. The shipping company will likely take one, US customs takes one, Canadian Customs takes one, etc....