As a seller you are listing on eBaydotCA, in US dollars.
When you look at your listing on dotCA you see both currencies.
When you look at your listing on dotCOM you will see only US dollars.
As a buyer, if you are bidding on an item on dotCA that was listed in CDN dollars you will see the price in CDN dollars.
If you are bidding on an item on dotCOM that was listed in CDN dollars you will see the price in both currencies.
And now I have a headache and will go lie down.