I think you're confused. There's no such thing as "Software Engineering" at UofT. That's a UW program. You're probably looking for Computer Science with the Software Engineering option (which you don't choose until second year). You'll be admitted as an Arts & Science student, but you're going to want to sign up for some MAT/CSC courses to fill some prerequisites for second year.

I was accepted to UTSG CS last year with a Gr12 average of 88%. I think their cutoff is much lower, though. Somewhere in the high-70 range. With those math marks, though, I wouldn't just worry about getting in. The math course for CS students, MAT137, is really tough. Way harder than high school math. If you're struggling with basic high school stuff, you'll be screwed next year. Your English mark is pretty important too, I'd work on that. English is required for pretty much every program everywhere.