Everybody bears a responsibility, but the primary responsibility is with the retailer. Why? It's not necessarily because the retailer knows, but because the retailer is the only one against whom the consumer can have recourse. The source is probably not even in Canada.
As to whether the consumer knows he's getting a good deal, in a dollar store you're dealing with somebody who might only be able to afford a dollar store. Do you think that person has enough sophistication to know that the authentic product is much more expensive, so this must be a counterfeit? Maybe that person isn't even aware of the notion of counterfeit. All that person thinks is, “I'm getting a good deal.” That person is relying on the store owner.
Incidentally, your question is one of product liability, and if I'm not mistaken—I'm not a product liability lawyer—the retailer is liable under product liability law.