It's really depends who you're calling. If you have US Google Voice number for your account (you can have one if you have US IP and just google for how to do it) and call anyone in US. They will love it because they could call your US number back and free long distance for them.
If you call them by using your Canada phone number, they will be charge long distance if they call you.
In either case, if everyone using Google Hangout to call then they don't really care as it is able to call North America free any way.