Just be sure whoever goes has their proof of UScitizenship. We never had any problems entering Canada. It's always been the return trip into US. One of our children was adopted from a foreign country. Apparently the US thinks blond haired people enter Canada to kidnap foreign born children-duh. Yet friends of ours who all have black/dark brown hair never got stopped entering with their child who was adopted from the same country as our child. We have never had any issues with food, but never brought fresh produce into US from Canada. I recommend you call and ask. Also our USCustoms stops were always in Niagara Falls area and they seem to stop people there alot more often than some of the other crossing locations.
Your son will be fine.
Kat