A big unsaid is that a lot of (white) non-Catholic families send their children to Catholic schools because they do not want them to mix with immigrants, in particular Muslims. Most English-speaking black Christians from the Caribbean and Africa belong to Protestant sects that consider Catholicism as heretics and therefore also generally shun Catholic schools. As a result, Catholic schools become relatively "white".
I think there is some truth that, as immigrants, your children should be able to assimilate better or at least have more chance to make friends with "mainstream" Canadians (however you define that term) if they go to Catholic schools. The same applies to French immersion programs. That is my observation.