Canadian here, who is also not a Trump fan. It is true that Canada has extremely lax border controls and there are complex organized crime networks that exploit this inside of and through Canada.
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.