> Is it enough for one person to consent or does something magic happen at a particular number or portion?
Nah. We have these things called elections (and representational democracy). In general that mechanism decides how society will progress forward from a political perspective.
The US government, acting in accordance with its constitution invades and occupies Canada. Congress creates 13 new states corresponding to the previous provinces and territories and elections are held. Almost all of the elected members from the newly annexed areas are opposed to the annexation and introduce a bill to allow the 13 new states to secede from the US but the bill is overwhelmingly defeated by members of Congress from the other 50 states.
Does the US government in this scenario enjoy the consent of the governed?
If they do, imagine that the original US population was more split on the issue so that the secession bill would have passed with Canada divided into 13 states. However the pre-annexation Congress anticipated this and resolved to make Canada a single state that would consequently not have sufficient representation to pass the bill even with the support of opponents from some of the other 50 states.
Does the US government still enjoy the consent of the governed in the second scenario?
Nah. We have these things called elections (and representational democracy). In general that mechanism decides how society will progress forward from a political perspective.