The US security establishment is aware of this, as is the Canadian security establishment. The 1% fentanyl headline is indeed widely reported, it’s also a red herring. The simple answer is Canada doesn’t really look, so not much is seen. More info here, by one of Canada’s best investigative journalists:
https://www.thebureau.news/p/trade-based-money-laundering-is...
IMO Trump is, as the official white house press release says, trying to put pressure on Canada to address this. Are tariffs the best way to do that? A valid question, for sure. Does he have other, possibly irrational, motivations? Also an excellent question.
But I see much Canadian and US commentary that assumes there is nothing rational about this at all, and that there is no Canadian border/security issues, and I would say that’s incorrect.