Hi! Former aluminum process engineer here. Caution– not a metallurgical engineer.

Really simplified version: if you recycle car body parts and cans and radiators and building metal, you can't make car body parts again out of them without diluting impurities down with prime (new) aluminum. So to recycle it is amazing, better than most products (since it offsets a TON of energy, way more than the same workable unit of glass or steel or anything). But just recycling doesnt fix it, you need some prime. Most of the US prime comes by way of Ontario, China, or Australia. Since a lot of the aluminum production is on the East coast in general, Ontario sees the most of it.

Seems like a very effective way to impact the US in response to the ridiculous tariff/trade negotiation situation

Having not yet read the article my guess is they ship it North to take advantage of cheaper electricity in places like Quebec

US recycles about 75% of their aluminum. Other countries it's close to 95%. But some aluminum alloys require virgin metal.