Yes, international roaming charges can be very expensive (both ways, Canada and the US). It's best to get an add-on to your plan or a pay-as-yo-go SIM from a Canadian provider.
With regards to food restrictions, things change all the time so we are never sure what's on the current no-no list. Lately we have been taking everything from our home fridge (after running quantities down to minimum in preparation for the trip) and if asked, declare what's in the RV fridge. If some of the stuff gets taken and dumped at the border it's not a problem for us as the disposal is free at the border but it costs us at home!