I have a US based ebay account and a Canadian ebay account. I actually prefer listing in US dollars unless promotions like this make it worthwhile, as it seems most of my buyers are from the US. When listing in USD, you pay less paypal fees, and if you have a USD account at RBC in Canada, you can just transfer from PayPal into the USD account without paying any conversion fees. There's threads on RFD about this.
Be aware that if someone in the US purchases your item listed in Canadian dollars, you will pay PayPal fees of 3.7% + $0.30. If someone in Canada purchases, you will pay 2.9% + $0.30 which is obviously the more desirable option. They'll get something from you either way. If someone outside Canada and the US buys it, you'll pay 3.9% + $0.30 which is the worst scenario.