That's how he aproaches a deal when he wants to negotiate. Starts with some absurd goal and if people follow the bluff, he will take it.
If people won't, he will try to negotiate half of what he has in mind and still claim a win. He's doing the same thing with Greenland.
But yes, i don't think Canada will ever become a 51st state. We talked about this and most Canadians will lose their universal healthcare.
Canada is a sovereign nation with its own culture and traditions so i don't think any politician up there is crazy enough to become the 51st state.
What both nations should do is re-negotiate trade deficits. This is the whole point of this rhetoric if you know Trump.
Once this is done then Trump will find something else to pick on.