Is the dog originally from the US and returning? Bringing pets back into the US is pretty simple. I've done it often from both Canada and Mexico. A rabies/vaccine certificate and rabies tag pretty much does it.
Or is the dog originating from outside the US with a change of ownership, like you bought it from a Canadian? That can make a big difference. The Feds are somewhat loose on this. Where you get into issues is the state that you drive into.
Well I just stuck a deal for a boy named Narys Policia. He is owned by a man in Canada and will be coming here to the US. I'm bring him back her with my truck so I do need to do my homework before going out there to get him.