eBay does not work like that.
Sellers, wherever located - Canada - USA - China - UK - wherever - determine the currency of the listing.
eBay.com will show US$ or approximate US$ equivalent for items listed in currencies other than US$ while
eBay.ca will show approximate Cdn$ equivalent for listings listed in currencies other than Cdn$.
Please note that the approximate value does not include the currency conversion fee charged by the payment service (credit card, PayPal, etc...), typically about 2.5% to 3%.
So if you see a listing in US$ listing on eBay.ca for an equivalent of Cdn$ 100.00 (for example), expect your credit card or bank account to be charged about $102.50 to $103.00, including the conversion fee.