The problem is, if you implement price controls, you're likely to end up with supply shortages. Canada grows food, but can it supply all the food needs of its entire population?

If not, then you have a situation like, suppose I'm a Mexican farmer and I can sell bananas to the US for $1.99 a pound, or to Canada for $1.25 a pound because there are price controls in Canada and they're not allowed to pay more than that. Why would I bother selling bananas to Canadians?

It's hard to control the economy like that because markets are self-regulating systems. Even if Canada controlled its entire supply of food, there are things Canada can't control, such as the price of fertilizer and farm equipment. If you put price controls on food and it's no longer economical to buy farming equipment and supplies anymore, you also end up with food shortages.