Rules, both ways change often. I have found crossing into the US stricter than crossing into Canada. Give the US border office were you plan on crossing a call a few days prior and find out what is the latest and greatest.
US Border http://www.cbp.gov/contact/ports
The Canadian Food Inspection Agency regulates what can be brought into Canada http://inspection.gc.ca/food/information-for-consumers/travellers/what-can-i-bring-into-canada-/eng/1389648337546/1389648516990
Generally I don't take fresh fruit or veggies into the US, any meat I bring I make sure is frozen. I make sure my pet food is in up-opened bags. Coming back to Canada has never been a problem.
Hope this helps
