Would annexation of Canada have ever worked out?

I remember that there were some US officials during the late 1800s who said this was a dream of theirs, but it never happened.

What if it had happened? Would it have been a net positive or negative for the two countries?

Would the U.S. have been able to maintain firm control of Canada by keeping their people happy and letting them have their desired amount of autonomy?

Would it have eventually broken down and caused a civil war?

Part of me says it’s too much land to govern, but then the other side sees that Russia has been able to hold on to their huge territories and not collapse. (Not yet at least)