On many of your listings you have just 2 shipping prices. On the ones you have listed on .ca it looks like you have 1 price for Canada and 1 price for the rest of the world including the U.S. On listings that you listed on .com, there is one price for the U.S. and another price for the rest of the world including Canada. I think that on one listing every country has exactly the same shipping price.
You can have more than one international option. Most sellers have 1 price for Canada, 1 for the U.S. and if they are using flat rate they have 1 for the rest of the world. If you are listing on .ca on the first interntational option, check off 'choose custom location' then click on the United States, the postal service you are using and a price. Then on the second international option you can click on worldwide or if you prefer, click on custom location and check off only the continents that you want to ship too. Enter the postal service and price.
If you are listing on .com you do the same thing except the first international option will be Canada, not the U.S.