I will speak about the members of the union I represent, because I know their situation best.
Not all international students have access to funding. Grant research funding is only available to the cream of the crop, whether it's Canadian or international. Federal government scholarships are available for international students to come to Canada, but only a small fraction of them have access to them.
Upon arrival in Canada, other students face not only the challenges of adapting to a new culture and education system, but also the lack of available support. Again, international students contribute a great deal to university funding, but don't receive the same level of contribution from universities. This would allow them to grow in the Canadian education system.