I don't know which shipping method to use. Help please.?

Hi I am trying to order something online and it is asking me which shipping method I want to use, they are all free:



US Postal Service

Canadian Post

International Air



I live in Canada does it matter which one I pick, and whats the difference?I don't know which shipping method to use. Help please.?
Well if you are trying to ship something to another country for free I would go for International Air because when you send like packages to other people by air it will take them less days to recieve those packages. Even though I'm not sure its free since I live in USA but if its free I would go for International Air.