If the executive branch led by the PM supported annexation, the opposition parties were split, Canadians themselves were divided and still the executive branch ie cabinet capitulated it would depend on what the crown decided.
It would be a mess but ultimately it is the GG as the representative of the Crown that would need to decide.
If the GG decided to ignore their executive and first minister and not support annexation then in line with all oaths of allegiance, the CAF, the ministers etc. should support that decision. If the cabinet refused then the CAF should still support the crown if we are looking purely at oaths of allegiance.
The CAFs allegiance is to the Crown not the government.