Earlier quoted context omitted.
The main reason the Dairy Supply quota is in place is to stop US dairy producers from dumping dairy into Canada. That's why the USA has never reached the tarriff limit. The big producers there would just dump 20 million litres at once if they could. They aren't interested in 1 or two. And if they were able to do that, the Canadian producers would go under. So its kinda simple, the Dairy Supply system is there to prot…
It follows then that the USA also wants to protect its industries, such as timber, oil and gas, and maple syrup, from Canadian producers that are happy to dump their stuff south of the border for cheaper than US competition.
I don't know about timber, but the US maple syrup industry is healthy, just unable to keep up with demand. I think that's a consequence of geography and the time investment required to get mature trees, not Canada undercutting.