I am going from Miami to Montreal 3-5 times per year by car. In the beginning with 2 big Labs, now with 3 little ones. I never had any problem with anything. I am taking my vaccination certificates for the dogs, as issued by the vet, and that's it. No one ever wanted to see them though. I guess if I would not have them with me....
At the border I get frequently complimented by the border patrols
or they just ask me how many dogs I have, or they ignore them. No problems with pet food either. That's probably crossing the border in both directions 70-80 times.