If you spend less than 48 hours in Canada, there’s a 3% tax added onto everything you purchased there above $200 total (not per item) at the border crossing. If you stay longer, it’s everything over $800. You do still have to pay Canadian taxes at the point of sale, and they’re not refundable.

You will have to have your food inspected at the border. All fruits/veg need to be inspected and can only enter if marked as a product of Canada. A lot of meats can’t enter. Exceptions are pork, chicken, and some beef if there’s proof that the country of origin in Canada. Meat regulations change frequently based on disease outbreaks, so they may be different each time. Prepackaged commercial food that’s still sealed is almost always allowed, but still needs to be inspected. Bakery goods and most cheeses are allowed.