People with rich parents who will pay for their education;
Toronto residents who can stay at home and wouldn’t want to leave the province;
People with significant commitments in the city, such as a partner or child; and
People very interested in NY Biglaw that are too dumb, unilingual, or broke to get into U of T, a T14 US law school, or McGill.
If there was a reliable way to predict success, I would add some categories (I think going to Osgoode has been a net-benefit for me, and I’m not in those categories). But there isn’t, so that’s it.
If money isn't an issue (by virtue of privilege, or self sacrifice of living rent free with family for 2-3 years) and you're interested in social justice areas of the law which lean heavily to hiring candidates who have demonstrated and practical training in those areas.
I'll let @BlockedQuebecois add more since he goes there, but that's how much I can infer based on what I know.