I just wrapped up my Undergrad at UofT, in Psych Major, Linguistics and Theatre Minors.
Classes to look out for, which will really boost your application are:
Research and Service in Communication Disorders - You'll wrack in a lot of volunteer hours in this one, and the work load is reasonable. You'll get to network with a lot of similar minded applicants.
Adult Language Disorders
Child Language Disorders
Start up on getting volunteer experience early if you can, and look in unusual places. UofT likes to see that you have experience with both adult and child populations. I received personal messages from profs from Western and McGill this year, because of the volunteering I've done in voice clinics (which is a smaller SLP specialty). Even consider emailing a researcher in the SLP department who's research you like, friends of mine have volunteered in the past, and say it's been a really valuable experience.