I did exactly this a few years back and it isn't an issue at all.
Loachman is right pick a unit in Waterloo don't waste anyone's with attach or transfer postings (which would happen if you applied for a unit that was based in Toronto).
All you have to do is call/email the unit and I say hi, I currently live in Toronto but I will be studying in Waterloo as of Sept 2016 and I am/not available for summer employment should it arise. . I want to join trade X. Then they will tell you no problem. You will likely have to travel to Waterloo (especially because you are applying as an officer) to do an interview/information session. The unit will then give you a letter, You then bring said letter to CFRC Toronto and they process your application as normal. Once your file is complete or September is looming closely tell CFRC Toronto to Transfer it CFRC Kitchener/Waterloo (not sure which it is but they will tell you) and the unit will either swear you in or you continue with your application.
Other Points:
- You may get a call (like i did) saying "uhh yeah we have an information session in 3 days we need you to be in City X for 19h. It may or may not happen but it could happen.
- If you chose to go back to Toronto for future summers make sure you tell your unit. Your unit will assume that you are taking the bus to CFB XYZ for the trade course from Waterloo but you need to either make arrangements for a POMV (Personal privately [1] owned military vehicle) approval or see if ops can get you on a bus from Toronto.) Either way the world wont end, but I'd suggest leaving your kit in your apartment should you go back home for future summers and then just take the GO Train to Kitchener and get on the bus with your friends. (1st 2 summers I went home to my parents place, first summer I paid a buddy all of his meals, a 60 of whiskey and a 24 of beer to drive me the base and got my mom to pick me up when the course ended, the 2nd summer I left my kit in my apt and went back to my parents, when I got the call I got on a train to the city where I was studying and then got on the bus with all my friends form my unit.)
- Likewise if your file is processed and they can load you on a course for this summer make sure they realize (tell them again) that you are in Toronto not Waterloo.
Lastly, make sure INF O is the trade you want to do, transferring trades once you are in the reserves is a pain, and you have much more mobility as a civilian. (Nothing wrong with INF-O, just make sure that it is what you want)
If you have any other questions post here (if i don't reply pm me).
Cheers
Édit [1] : thanks Mario and George