Typically, businesses always charge their 'home' currency, so if the shop is in Canada, you will pay Canadian Dollars. Normally you don't have any choices either.
Your credit card company will convert it to your currency, using the current international currency exchange rate (pretty good), plus a potential fee between 0 and 5% - depending on your credit card (not so good).
If it is a significant amount, or you plan to do that more than once, and if you have multiple credit cards, check first to see which one has the lowest international fee; 0% is not uncommon, but neither is 3 or 4%. If it's a 10$ thingy, it's probably not worth the time; but 4% of 1000 is already 40$...
As of right now, the currency exchange rate is 1.33, so you would pay ~75 USD; plus the potential fee, 0$ - 4$. Understand that this exchange rate is floating continuously; it probably won't change much, but it will change.