A US invasion of Canada would be militarily successful but result in absolute nightmare chaos. There would be a global move away from US trade, financial, and military cooperation; you'd see tons of rearmament and new nuclear weapons states; the US military would lose its logistical network as countries kicked out bases; the global economy would crash; there'd be a supply chain fire worse than 2021-2 as trade shut down; financial systems would get set on fire as the dollar lost reserve currency status and on and on and on.