Apparently, young-uns today do not know what the Schlieffen Plan was. When Germany attacked France, they went through relatively undefended and relatively weak Belgium to reach around the French flank. The Belgium-France border was undefended. Any country seriously thinking of invading the US would first attack either Canada or Mexico, then go through and attack the US through this relatively undefended border, instead of attacking the US directly. The ONLY reason another country would even think of attacking Canada would be to just pass through and attack the US.
If the Americans did not stop them in Canada, the entire US would be vulnerable. The US-Canada border is just too long to defend completely. That was the entire purpose of the Ogdensburg Agreement.
Sometimes it is very difficult to tell the difference between human-generated and chatbot-generated responses.