Unless you are shipping from the US you can't use calculated shipping on .com. When I do list some items on .com I will figure out an estimate for shipping within Canada and set one flat rate just for here. Then I set a rate for international destinations based on the cost of shipping to Australia or the most expensive place that I ship to. If you use 2 different services such as standard international for Canada and economy international for other places, the rates will show up separately on your listing.
If you want to ship just to Canada and the United States or want to block specific countries you can do that on your shipping preferences page by setting up an exclusion list which will block people with addresses in specific countries from purchasing from you. You can also block specific countries on your listing page.