how do i determine the currency of purchases

As Apple's Terms of Sale only permit you to have an iTunes/App Store account in a country where you have a legal address and they also require that credit/debit cards have a billing address in that country, all iTunes/App Store purchases are in your local currency.

Apple's iTunes and App Stores are region based. Any prices shown are in the local currency for the country set for the Apple ID region.

If your region is set to Canada, and you are using a Canadian credit card (which you must be using, as it won't let you use cards with billing addresses in countries other than the one the Apple ID is set to), then prices are set to Canadian dollars.

See here to verify your Apple ID's region: Change your Apple ID country or region - Apple Support

Nope, if you have a Canadian credit card registered to your Apple account, it is charged in Canadian $$$.

Then it sounds as if you're using a U.S. account. Did you move from the U.S.?

Ok.