On the food issue... Coming North will not be a problem... We are far more relaxed up here and recognize one bag of dog food will not destroy the countries Ecosystem
You can also bring your "Human" Groceries North as well. Returning home be prepared to dump your dairy, meats and vegetables prior to arriving at the border.
We cross the border several times a year with the dog and never had an issue. As others have said it will be going back into the US that will be your problem. We keep a tupperware container full of food for the dog. But when we are crossing we also bring a small unopened bag with us that indicates it was made in the States, that way if they do make us dump the bin we at least have a few days worth so there is no rush to find the pet food store.
The only other time food can really be a challenge is if you are on a Raw Food Diet. If that is the case, plan on having to re-buy your food after re-entering the States.
Final point... We cross a Niagara Falls most often... They have never asked for the dogs papers or inspected the food. I suspect it is a product of how busy they are and the fact that they are not in the middle of Farm country so Agriculture is not their primary concern.