I list on eBaydotCA because most of my listings are books (not on this ID, I have several) and on dotCOM my shipping would be capped at $4.00.
But I only use loonies when my item is unlikely to be of interest outside of Canada. For example, my mint postage lots are in Canadian dollars, but my Newfoundland covers which will sell internationally are in USD, even though the Nfld Specialized Catalogue is in CDN.
Remember that if you have a shipping fee to a given country, whatever you list in, the view in that country will also see your price in their currency.