The good professor is ignoring the fact that Canada has a lot more to lose than the US.  Just for starters look at the balance of trade Canada needs the US more than they need Canada.  
As for their arguments Trump probably is correct about the dairy thing.  Many Canadians show it when you see them with shopping carts full of milk they are bringing back from Costcos in the US.  What Canada has to realize is that what is needed is give and take which means some good negotiating tactics that I dont think the Libs have the skills to perform.