Assuming you mean to sell on the Canadian platform and are shipping directly to buyers (not FBA), then you must ship in such a manner that the buyer does not have to pay any sort of customs/import duties. This means you cannot use USPS, but must use a carrier where you can prepay (or sell only low value items that come under the threshold).

If you mean to offer your listings on the dot com site to international buyers, then it's a whole different answer. In those cases buyer is responsible for any customs/import duties or fees.

In either case, you set shipping charges through templates.

Do not start something you don't understand -- don't jump into selling in Germany without knowing about about EPR (this just one example)