I do realize that. The war in Ukraine is not being supported by Nato. They are sending supplies but the alliance is not entering Ukraine against Russia so as to not create a wider conflict. Note that Ukraine is not a NATO signatory while Canada is. In the case of the US annexing Canada,the strategic analysis would give two options. Either immediately oppose US aggression and form a bloc independent of them, or tacitly approve of it and leave yourself open to the same thing happening to you and your neighbours.