See, this is what happens when the purists get challenged with facts.  They have to move the goalposts to errrr, mostly-ish-white/mostly-ish/judeo-christian.  It's absurd.  You asked for an example of a mono-culture, so I'd say Japan in the 1800's is a rather good example of a mono-culture.  Canada never has even closely resembled a mono-culture in any sense.  Goodness, we can't even agree on a unified legal system.  We have aboriginal peoples and a French population that claim to be unique nations. within Canada   If the French believe their culture is distinct from English Canada's, then that is two rather large cultures in Montreal as it is.  Honestly, if you are to define Canada in the 1950s and 1960s as a mono-culture, than every country on earth is a mono-culture.  Takes away the meaning of the word altogether.