Check your local telephone directory. The stuff you want is used for making the tarps which cover loads hauled on flat-bed trucks.
These tarps are sewed and sold by hundreds of 'tarp shops' across the US, and I would assume the marketing is similar in Canada.

If you can't find tarp dealers in your telephone directory, look for trailer dealers, or truck dealers who sell big rigs. Many of these sell trailers, or have a business connection to a trailer dealer. And the people who make and sell tarps for trailers leave their business cards at trailer dealers. A few phone calls should get you in touch with someone who will sell you a few yards of PVC coated truck tarp fabric for covering your kayak.

Hope this helps.
PGJ