The Greater Toronto Area which includes Mississauga, is huge, something like 6 million people. But in elite sports, I am sure players at least know of each other, and probably know each other - AAU, regional and provincial championships, tournaments, etc. So, while Mississauga is a biggish city, I am sure Naz and Jankovic at least know of each other, if not know each other.
They were on the same AAU team as somebody already posted.