Further to my articles here, here and here regarding trade and NAFTA, I came across this interesting Toronto Star article, which describes the truth about the oversupply of milk production in the United States.
 

Source: The Toronto Star

Canada already controls its Canadian milk production to ensure that its producers can sustain a living, while adequately satisfying its domestic demand. It's no fault of Canada that the U.S. has not done the same with respect to its domestic production and consumption.

It's notable that President Trump would rather try to bully Canadians into buying more than they need by forcing U.S. dairy products on them, rather than addressing his own domestic oversupply issues, or look for other export markets. As I mentioned previously, Canada has a population of only 36.95 million versus 327,867,715 (on June 7, 2018) in the U.S., so Canadians can consume only so much milk, compared with Americans...they don't need to be force-fed more. And, they certainly don't need to be ordered to consume American products or be threatened with auto tariffs if they don't comply with his bullying whims.

So, Mr. Trump, don't blame Canada for your country's own mismanagement issues. It appears as though some Americans are already studying a proposal for a "Sustainable Milk Inventory System Act," which has been summarized as a "U.S. version of the Canadian system with improvements," as noted in the following excerpt from the above article. Perhaps you could learn a thing or two from your own farmers, who are actively seeking solutions to their problems.