If you are searching on the dotCA (Canadian) site, items show in Canadian dollars even for sellers who list in US dollars.
If you are searching on the dotCOdotUK (British) site, items show in British pounds even for sellers who list in Canadian dollars or US dollars.
If you are searching on dotCOM (the US site) items show in US dollars as well as the currency the item was originally listed in.
If you are only seeing US dollar prices, then you are seeing items listed in US dollars on the US site.
Which leads to the question, if you are so determined to shop in Canadian dollars, why the are you looking at the US site at all?