Obviously, Canada doesn't have the best farming conditions. Short growing season, bitter cold, etc. It makes sense that some powerful lobby for the farmers got a set of blanket import tariffs passed in order to smooth out the seasonal gap between them and say, Kansas. Then, over time, they were free to raise their own prices. It's definitely not a good situation, but it's hard to remedy after such a system becomes entrenched, short of subsidizing their own citizen's food purchases.
Economically speaking, it's similar to a smaller downstream agrarian society in a larger water-monopoly system. Only real difference in this case is that the coin is fecundity instead of water. Without impartial balancing and distribution, great inequities arise. Right, Texas?
NOT getting into politics here. Just supply, demand and the consequence when you open up the local market to larger suppliers.