If you are willing to steer away from bigger chains such as Loblaws, No Frills, Sobeys in search of slightly different produce and not private label supermarket brands such as PC, Compliments, No Name, then I highly recommend Highland Farms.
If you have a special penchance for Polish, German, Italian foods, but have trouble finding a shop that carries a lot of these varieties in GTA, you may actually find yourself satisfied shopping at Highland Farms.
If you need eucalyptus candies, sauerkraut, sausages, smoked whole fish, Dutch waffle cookies, Polish chocolate wafer bars, pistachio ice cream, good havarti options, and a few slices of summer sausage and headcheese (And you know what is HEADCHEESE!), then you must make a visit to Highland Farms.