Contrary to popular opinion, there are no liability or legal barriers which prevents supermarkets from donating food. The Food Donations Act absolves liability from food donors.

“While the legislation varies province to province, generally speaking, across Canada it is completely acceptable to donate and distribute food to another person without being held responsible for injuries, illness or death unless the food is rotten or unfit for consumption or is somehow unsafe to consume. If donors, which could include grocery stores, are acting in good faith and donating food that is safe for human consumption, there should be no issues with donating leftover food products.”- Priyanka Vittal, Legal Counsel of Greenpeace Canada

You can check out the provincial bylaws on page 4 of this document: http://www.nzwc.ca/Documents/FoodDonation-LiabilityDoc.pdf#search=food%20donations