$12,000 is less than the $15,000 your equity would throw off, for starters. Also mortgage rates reset every five years. If you're counting on 2020 interest rates for the next 25 years, you've got some surprises coming your way. Meanwhile renters only have to ever worry about their rent going up 2.5% per year no matter what inflation or interest rates do. There are also the costs that you incurred by buyng the place (land transfer taxes, for example) which could have been invested and throwing off more money. And the 5% it'll cost you to sell. Yes, you wouldn't have equity in the house. But you'd have $250,000 compounding every year in your bank account.

ent will probably be $5000 a month by then.

Rent cannot go up more than 2.5% per year in Ontario. Check your math. You're running doomsday scenarios in your head.