A person has to be careful when identifying an original versus the reproduction bodied open cab commercial or truck types post model A production. There are now reproductions that mimic the original but are not the same. The windshield and rear cab usually give them away. The production figures were a little over 700 units when Ford stopped production of the open cabs. With production that low, they were likely using up bodies that they still had on hand. There were still some Ford fans that preferred the open cab prices and some may have been for fleet use on special order.
I'm not sure about Canadian production. They may have made them longer.
My great uncle had several open cab Ford model B vehicles while he was in Kenya in the 30s They were preferred for hunting vehicles and used a tarp type top to cover from the windshield to the tailgate with seats fabricated to fit along the bed rails.