I think most universities give single rooms to the other years (Not first years). Or at least that's what it is for UBC.

depending on the school you go, Carleton has alot of doubles but you can get a suitstyle room where everyone gets their own room but you dont miss out on the social aspect of res.

The upper year students get first pick; but if there are any single rooms left over, you can have one :) I lucked out with a single room my first year! A LOT of students drop out after christmas, so you can might end up with your own room anyway if your lucky. You could always apply to be room mates with an exchange student. They don't stay for the whole year, so you'll have to share your room for half the year, but get it all to yourself the rest of it!

It depends on the university, but most that I know, it goes by lottery if you want a single room..
Most first years are paired with someone just because it IS your first year and it's easier having someone there you know since you will know virtually no one.
But if you put in a request for a single room, it goes into a big lottery and you just cross your fingers and hope you get a single!
I don't know if it works that way for all universities, most, I'm guessing.