Can I buy an iPhone in the United States and mail it to Canada as a gift?

Once purchased from Apple, you can do anything you want with it. Though Canadian customs may charge the recipient import fees.

If you mean, can you ship it directly to Canada from the US Online Apple store, then no. Apple will not ship outside of the US when buying from the US Online Apple Store.

Also, note that the warranty will only be valid in the US, and the iPhone will need to be brought back to the US for any warranty service.

You can buy one directly from the Canadian online store using a US credit card, and have it shipped to a Canadian address however.

Fine as long you personally and physically buy the phone in the U.S. yourself and then mail it to Canada.

No go, if you are asking if you can buy the phone in the U.S. either in person or online and have the seller ship the phone to Canada.

In either case, you should not expect the warranty to be good in Canada. It might be....that would depend on the policies of the service shop in Canada.

The "golden rule"......you should buy the phone in the country in which it will be used most of the time......even if the cost might be higher.

A phone should be purchased in the country it's intended to be used in. There is no such thing as an international warranty. Should the phone require any warranty work, it would have to be mailed back to the U.S.