You should find all the information on demographics if you were to look up St. Catherine's on Wikipedia:
St. Catharines - Wikipedia, the free encyclopedia I'd also imagine you could find a whole lot of info on the city's official website:
The City of St. Catharines
In general, multiculturalism is an important aspect of Canadian identity as Canada is a nation of immigrants, so even if you move to a town with a more homogeneous demographic, having a multicultural family won't pose any problem.