Many eBay sellers in the U.S. post listings that say "Will ship to US only". I often email sellers, for items I'm interested in, to ask if they will ship to Canada. Most will reply "no problem, they will ship to Canada", but some say "no way".
For the record, there are around 35 million people in Canada and I'm sure a good percentage of them have heard of or use eBay. Is it a good business practice to cut off millions of potential customers from your auctions? You are also cutting off the rest of the world from your auctions as well, not just Canada. eBay is a world wide phenomenon, so you should be ready to deal with a global marketplace. Last year, in one week of selling a few items on eBay, I had one sale to England, one to France, one to Australia, one to Canada, and two to the United States. If I said I would ship to Canada only, what would that have done to my sales?
If you are in the US, and are willing to ship to Canada, please change the checkbox for "Ship to locations" when listing your item. You only have to do it once and then eBay will remember that preference.
As far as payment options go, many of us Canadians use PayPal just like your American buyers do. This means you get paid just as fast, in U.S. dollars, exactly like you do from anyone else. Another option for Canadians to use is BidPay, which is an alternetive online system to PayPal. This can be paid for with a credit card online. The service is quick, easy and secure.
Yet another option that I use for small transaction amounts is to simply mail U.S. currency in an envelope to the seller. I have done this many times without incident. I make sure to have at least 2 sheets of paper folded around the bills, so you can't tell they are in the envelope. I have also received payments this way from around the world without any trouble. The only drawback is that you can't really include any coins, so you have to round the payment up to the next dollar. Sometimes you can negotiate a reduction in shipping and handling charges with the seller. Since you are paying cash, the seller avoids the extra fees from PayPal, and thus makes a bit extra on the auction. This is a bit harder to do for deals within Canada (paid in Canadian dollars), since we have $1 and $2 coins instead of bills. It makes it hard to get small amounts in just bills.