I may have to do with production volume as well. I don't know the relative amounts between Ontario and BC, but we have a similar situation here in the States. Because California produces SO MUCH wine, it is everywhere in the market. Most people don't know it, but there are wineries in nearly every state (I think Alaska is the only exception). But, if you go into the stores, most of the US wine you find is from California.

Also, the wholesalers don't want to deal with small volumes. They would much rather deal in a California wine that produces, say 500,000 bottles or more a year, than a wine that produces only 50,000 a year.