Canada doesn't have a more homogeneous population. And I doubt England and France do.
And why would the size of the population matter?
Poverty maybe - but shouldn't the richest "free" country in the world have less poverty rather than more...and is poverty really a factor? Kliebold & Harris, Cho, Charles Whitman, most (or all) of the others weren't poor.
I agree Euro countries are quite different than the US but maybe those differences are the key to figuring out why things seem to have gone so wrong here with regards to gun deaths.
And Canada, superficially, IS a mirror of the US and its gun deaths per capita are nothingn close to those here.