Legally, in the US (I'm assuming the same is in Canada), you cannot exclude anyone as a tenant based on race, ethnicity, and a bunch of other criteria. You can get in BIG trouble for playing any of those games. UNLESS you are talking about someone co-habitating with you. You're the landlord and you're renting out a room in the home you live in. Nobody can make you live with someone you don't want to.
That said, it happens. It's stupid when it happens, because the landlord is treating his business as something other than a business and letting his personal opinions get in the way of business, but that's their choice. Some ideologues feel that making money in business is so easy that they can place ideology ahead of business and still do well. That's called stupidity. Leaving aside legal issues with acting that way, you're going to screw up your business doing things that way. It's just dumb.
There have also been some comments about "well, I rented to this guy and it didn't turn out well". Well, duh. CHECK THE DAMN REFERENCES. Call people. Get multiple references, get multiple sources of information. You legitimately handed the keys to a property worth, at minimum, six figures without checking the damn references? Are you flipping INSANE? It's one things to TOFTT for a $300 SP, but to TOFTT with a condo or house? Oh, I'm sorry, were the three phone calls you'd have to make too much work to make a couple of thousand dollars a month, due at the first of the month, every month?
I'm a landlord. It's the easiest damn job I've ever had, and I was a movie theater usher when I was a teenager (take tickets, close doors, take a 2 hour break, open doors, repeat). But you still need to get a couple of basic things done to make that easy money.
Housing discrimination is:
1.) Against the law.
2.) A stupid business move.
If you're in business to do something other than make money (and have fun while you're doing it, but the money is the crux of the business), then you're just being an asshole.