Donald Trump wants an open border with Canada. At least, that's what would happen if Trump were to execute his stated preference for annexing Canada as the fifty-first state. 

In recent days, president-elect Donald Trump has made a number of comments suggesting that Canada should be annexed by the United States as a new state. For example, on Tuesday, Donald Trump told reporters at a press conference that the U.S. and Canada combined into a single country "would really be something." This followed an earlier X/Twitter post in which Trump listed a number of benefits to Canada and concluded that "if Canada merged with the US" the resulting union would be "a great nation" 

This depends on what one means by "great nation." If the goal is to move the United States further to the left ideologically, and to make the US more like California, then yes, adding Canada as a new state would certainly be a good thing. For people who like freedom, on the other hand, it's not a great idea. 

The sort of MAGA voter who thinks this is a good idea is not exactly strong on critical thinking. Those who are capable of thinking things through, on the other hand, might notice that adding Canada as a new state would create an open border with a country of 40 million Canadians, most of whom hold political views well to the left of the average American. It appears that some of the same conservatives who complain about Californians moving to their states also want to open the border to a new California-sized state to the north.