Exit Tax

Generally it's true that it is included in the taxes when you purchase your airline ticket. Especially for regularly scheduled flights from Canada & USA. But if you enter by land and don't pay it then, or while in the country, and then try to fly out, you'll have to pay. Sometimes if you leave by land or boat, they'll request proof that you paid. If you arrived by air you'd have to show them your full receipt for the airline ticket as proof. Sometimes charter airlines don't include it in the ticket price.

But generally speaking, flying in from Canada or USA and flying out, you're unlikely to have to pay anything when leaving.