I don't think that argument holds: Canada is a pretty diverse place but I don't think there are simmering/barely-contained tensions there as much as in the US.
I think a lot of the tension results from specific 'environments'; in reverse chronological order: the "southern strategy", Jim Crow laws and ultimately chattel slavery. For most of its history, the prevailing, unquestioned belief was that one race was inherently superior. It will take several generations to rollback that mindset back to any significant degree