People here are giving you some pretty ignorant ideas. The reasons things like this exist for certain industries in Canada is to maintain healthy markets while protecting the smallest of players in those markets. Things like Maple Syrup and Milk are tightly controlled because it ensures that in both good times and bad that the market does not get too volatile and squeeze the smallest producers out of it.

Usually the strongest opponents of these controls and regulations are the giant players or external interests that either want to be able to dump product to undercut and corner the market or eliminate the ability for any industry to collectively bargain for better deals when it comes to things like shipping infrastructure (take railways as an example).

And then there is Canada's proximity and cultural similarity to the United States, which while being it's greatest strength is probably its greatest weakness. The USA heavily subsidizes its primary industries that it is in Canada's national security interests to keep up high walls, regulations, and "cartels" to keep things like Canada food security in Canadian hands.