Farmer 4321 you actually described the differences between the Canadian and US system well.  Supply management is not perfect, but it does regulate the supply to avoid subsidizing.  Trump is just using it as a talking point to his base.  It is true that the tariff is high, however both countries are basically suppIing their own market, and one way or money is getting paid to keep dairy going.  I heard that there is more dairy in Wisconsin than the entire country of Canada!  So even if dairy got renegotiated would this solve the overproduction in the US?  Not likely.

However if trade deals or talks fail, it is probably a good idea both countries have a way of making their own supply, with Canada being a lot smaller of course.