printed on the gum side.
not totally sure how they do it in Canada, but usually the sheets are gummed after printing, which means the gum is on the front, over the ink.
again, not being familiar with Canada's production process, I can only relate my experience with Serbian errors of this type. The design will usually appear faded and less sharp, as the gum coating mottles the design. Also, the front side will have the tackiness of the gum quite obvious.