That would be impossible for Trump to pull off politically. I don't say he won't speak in a threatening manner to Canada sometimes, I am saying that it would disrupt the USA's economy and the world's stability too much if a spread north with American troops was tried. Goods must flow smoothly over that border for both the USA and Canada to survive economically. Also, the American public have a "favorable" view of Canada at this point. So, I am not saying there won't be a political battle here and there for the two economic partners. But American troops won't be crossing that border.