Congratulations on your acceptance to Queen's! I am doing my undergrad at Queen's right now, and you will love it here!
If I were in your situation, I would wait until the deadline to accept/decline the offer from Queen's to see if you get an offer from UofT by that time. If you don't hear until that time, I would probably accept the offer from Queen's anyway just in case I don't get accepted by UofT.
Accepting the offer doesn't necessarily mean that you HAVE to go to Queen's in September; if you get accepted by UofT, you can always notify Queen's and accept UofT's offer instead!
Good luck with your choice!