That tariff Canada applies on US dairy is designed to only kick in at an annual amount that has rarely been reached. It’s designed to prevent subsidized American dairy from flooding the Canadian market thus killing the Canadian dairy industry. No different than any other nation would do to protect it’s national interest.
One point many/all miss is the big picture. America wants safe, stable neighbors whom they can rely on an trust. Since the 1930’s America has recognized this and worked with Canada. We have both benefited. What’s happening now is Canada is being pushed into other market’s, which opens the door for other Countries influence and ideologies. That’s NOT good for America. There seems to be no "big picture" thinking in the current administration.