[@Legion-114]
I don't have an issue with Super Mutants having spread north towards Canada, though I find it unlikely that one of the few intelligent Super Mutants would be accepted by anyone, if anything they'd be shot on side. The pre-war world is more of a shoot first ask questions later type of world, especially regarding something as a Super Mutant. 

I can however see one intelligent Super Mutant leading a band of dumb Super Mutants and using them to raid inside Canada, though this would imply a faction being present rather then loosely scattered groups of Super Mutants we could encounter.

As for the Synths, the Railroad helped Synths yes, though mostly to neighbouring states. Their objective was to get the Synth outside of the borders of the Commonwealth, from there on out they were on their own. (Might be slightly wrong here but i'm fairly certain it was just getting them outside of the Commonwealth.) Their memories were wiped as well, hence their knowledge of the Institute would be gone also. 

Even if one went to Canada, northern Canada in the east that is. It is very unlikely that they went all the way to Vancouver in the West, even more so if one got their alive.