Hey, first of all, you need to realize that the biostatistics program at UofT, although is adequately competitive, it considers individuals from different backgrounds (i.e. biochemistry, kinesiology, computer science, statistics). Anyone can apply taking any courses, but obviously, individuals with the recommended course list mentioned above will have their application strengthened. The graduate office takes this into account, so you can pretty much take anything in your last year.
I think this is general basis of their decision. The year before my last year, my sessional GPA was 3.0 (pretty damn low) and I did pretty badly on my thesis taking primarily biology/biochemistry courses. In my first term, I took all 2nd/3rd year mathematics and statistics courses (calc, lin. alg., mathematical stats, introductory probability) and a bird course and ended up with a term average of 3.94. I eventually got the offer mid-March.
So from this experience, I think your term 1 marks for your final year will be very crucial no matter how low you got in your previous years (it plays a role obviously, but not to the extent you might have thought) and if it's math/stats courses that's an added bonus.
Your references also play a big role. Make sure the references can describe how you will succeed in the program and how this Masters degree can benefit you after you've graduated. (Degree should be a stepping stone towards your end goal).
In my opinion, your statement is the most important component. It should reflect how driven you are. Have it edited a lot and make sure you show your conviction. Imo, a good statement of interest will highly increase your chances even with bad marks.
International acceptance is hard everywhere and Toronto is definitely the hardest school to get an acceptance from just in general (for biostatistics, maybe Western's program too, but that's only because 10 people are enrolled a year) just because of how acclaimed the place is. The other reason Toronto is hard is because of their very applied heavy program; designed for students to develop practical skillsets through very applied heavy courses and a practicum. Students who graduate often work as biostatisticians right away from what I've heard. To answer your question, yes your chances will be low, but to be honest, if you are a good candidate in terms of marks/statement of interest, every school you apply to will be easy, so apply anyways.
But keep in mind that with a MSc. in Statistics (which is easier to get an acceptance from), you can basically do the same thing career wise. MSc. in stats will be the theoretically heavy route, which is useful in many other ways. Many people who graduate with MSc./PhD in Stats at York/Mac still do biostatistics-related work so this isn't a bad option either. It also gives you the freedom to do actuarial/financial statistics if you decide to shy away from biostatistics. This was what I was debating with vs. Toronto, but I chose Toronto for the nice food/active social community.