You're asking the wrong question.
The real question is why the they aren't higher?
The U.S is the most powerful nation in the world. You either get on the train or get off.
If Trump was the dictator/king that libs here think he is, that's precisely what he would do.
Trump clearly has what he feels is credible evidence that Trudeau and the politicians running Canada are controlled by China. So he wants to take over Canada before China does.
Canada cannot survive without US trade. It accounts for 20% of the nation's GDP.
Trump raises tariffs to Canada to attempt to et Canada to tighten its border. Note Trudeau refuses. Is that how an ally responds?
Trump is going to gradually increase tariffs to help make the case to the Canadians that Trudeau is compromised.
And it's going to work. Recall in his inauguration address, Trump talked about how the US is about to enter its Golden Age, but he also mentioned how the US is about to EXPAND.
By the end of his term, the US will control Canada, greenland, and the Panama Canal.
PS: Hey libs...when Trump starts really drilling home the message that China controls Canada and how they are the enemy, pay CLOSE ATTENTION to which politicians come out of the woodwork claiming that CHINA IS OUR FRIEND. Those are the guys bought and paid for by China.
Trump always has a plan. 4D chess, as
@GatorTheo correctly said.