The Canadian Food Inspection Agency says the affected products may be tainted with a bacteria (Vibrio parahaemolyticus) that may result in vibriosis.
The affected products were sold between July 3 and Aug. 6 at a variety of Loblaw, Real Canadian Superstore, Sobeys and Zehr stores in southern Ontario.
Those products, which were also sold by certain retailers in Quebec, include blue point oysters or Atlantic oysters, littleneck clams and cherrystone clams.
Consumers unsure if they bought the seafood should contact their retailer.
The CFIA says the Canadian importers are voluntarily recalling the affected products and the agency is monitoring the effectiveness of the recalls.
Officials in Connecticut have recalled oysters and clams from certain harvest areas, saying they were implicated in a number of illnesses in the U.S.
There are no reported illnesses linked to these oysters and clams in Canada.
Food contaminated with the bacteria (Vibrio parahaemolyticus) may not look or smell spoiled but may cause vibriosis, a food borne illness.
Symptoms include watery and-or bloody diarrhea, abdominal cramps, nausea, vomiting, headache, fever, and chills.
Severe illness is rare and is more common in people with weakened immune systems.