Agreed.
Anyone coming to Canada has to travel by air, sea or swim if they're obliged to `try'. Only the latter would be a person that is `sneaking into Canada'; the first two would be vetted, to some extent, before being allowed to enter Canada, greatly reducing the chances of a hardened criminal, carrying a bag of Fentanyl into the U.S.
Well, there is the unregulated land border crossing issue, by which I'm including getting across certain areas by boat, etc. Which is a fairly big number, and a fairly big deal.
But much larger in the opposite direction, from Canada into USA, and my understanding is that the cooperation with US law enforcement is very tight. Of course law enforcement on both sides complain about budgets/not enough toys, lack of legal mechanisms they'd like to have, and blame the other guys - at least a bit - but everyone knows it's very tight cooperation.
There are also just logical/legal limits on both sides: we don't have (on other side) large 'border zones' that private citizens are forbidden to enter, and for the most part, you're not breaking a law in Canada if you just happen to be near one (proving 'intent to cross a border illegally' is not so easy, in other words). They try to track the known traffickers and things like that, of course. But at some point, sometimes, they are forced to just follow and provide info to their counterparties across the border, who try and pick them up. Which both sides do pretty efficiently, but we all know 100% isn't possible.
For fentanyl and guns, we know a lot of the problem is just that we have a free trade regime and enormous amounts of trade, and they can't inspect everything. Yep, lately it's gotten worse. (Fentanyl as I understand it - the issue is that on a sheet 'doses per unit of weight' basis is something like 1000X more concentrated than even things like cocaine. Tiny amounts. A zillion times harder to catch than, say, cannabis).