I’ve lived in various provinces in Canada. West of Ontario I really only see the waxed-paper cartons or the plastic jugs, stores carry both equally. Eastern Canada carries the plastic bags (and everyone has a plastic container at home they place them in after snipping the bag corner) and often the cartons. Bit weird the custom changes across Canada, and coming from the west I was very confused about the bagged milk when I first moved to Ontario.

Maybe someone else can comment on their experiences. I’ve never seen bagged milk in a store in the prairies (but I only lived in major cities).