We of course respect our neighbors’ sovereignty and immigration laws in the way a *certain* neighbor does not.
The deal as I understand it is that the US and Canada have signed a treaty stating that both recognize that neither politically oppress people, and that refugee claims from either country are invalid.
The upshot of that is apparently if you drive up to a border post and announce that you are a refugee they have to refuse you entry. So the only way to claim refugee status is to enter illegally. Then it becomes a gray area because they can’t prove that you entered illegally from the United States.
But Canada's current policy is,it would appear,that if you succeed in entering Canada by sneaking in illegally (that is,not at an official crossing point) you can remain in the country at least temporarily and *possibly* be allowed to lodge an official refugee application in Canada.
I'm not sure what you mean by "a certain neighbor" but I think that comment is unwarranted...at least from a legal standpoint.
Of course Trudeau wants to embarrass and belittle Trump.Just about every leader of a Western nation wants to do that now.But no leader has a legal obligation to support a particular US President...although failing to do so can certainly be considered "unhelpful".