Does the president have unilateral authority to apply tariffs or does it have to go through legislation?
Basically... yes. It does have to go through legislation, but the issue there is it's
gone through legislation and the legislation broadly left the president with unilateral authority to apply tariffs.
It's a power designated by congress that could be removed or overruled by congress, but fucking
lol at the prospect of the incoming congress being willing to shit in trump's sandbox like that. It's ostensibly possible, but practically incredibly,
incredibly unlikely (so long as there's a GOP majority, so at least until 26, probably).
Canada is shocked with Trump's annoucement it will get 25% tariff rates at the first day of his presidency.
I wonder if Canada (and Mexico) will have balls to respond with simmilar tarrifs.
Mexico's already been quite loud that they will retaliate, and their current leadership would be pretty damn certain to follow through with it. It's... not likely Sheinbaum is going to be particularly cordial towards trump, for a gigantic host of reasons.
Good bit of canada's political critters across their entire spectrum has also been making noises along those lines.
That said,
similar tariffs are unlikely -- the last time trump tried tariff horseshit with those two, they used very specifically targeted retaliatory tariffs to basically rile up folk stateside so badly trump functionally went and rolled over, belly up. They, unlike trump, aren't stupid enough to think a universal tariff is needed or helpful to accomplish their goals, so it's fairly unlikely you'll see
that. Retaliation, though? About as close to certain as certain gets, and it's going to be aimed to hit where it hurts.