So they’ll be just like all other students in the US and Canada, then?
OAC, for those who don’t know, is (to put an American spin on it) an extra year that Ontario students spent at high school. You graduated an Ontario high school after five years of study, not four. OAC is no longer necessary for Ontario students, hence mnemosyne’s statement. But my view is that if Americans and Albertans and Manitobans and so on can go to university after four years of high school, why can’t Ontarians be expected to?
By the way, mnemosyne, this is just an opinion, and I’m not looking for a debate–I’ll defer to your knowledge of the current situation in Ontario schools and universities. It’s been a long time since I’ve been a university student (twenty years, in fact), but since nobody else has posted anything for Ontario, I’ll give it a try.
I don’t know why the term “OAC” is used; when I was in high school in Toronto, we called it what it was: Grade 13. You could graduate with a Grade 12 diploma, which would get you into community colleges and the like. Students who opted to continue to Grade 13 were generally expected to go on to university.
To get into an Ontario university in those days, you only needed high marks in your Grade 13 subjects. Once again, you needed high marks. And did I mention that you needed high marks? 
Seriously, that was all you needed. There were no SAT requirements, extracurriculars counted for nothing, no interviews with university admissions staff were required, essays weren’t needed. High marks, and high marks alone, got you in. And you did not need to declare a major before entering; that could wait.
One requirement that came in at the University of Toronto a year or two after I started there was this: once accepted to the U of T, all first-year students had to write the English Proficiency Exam. There were some whose English skills were not adequate for university study; this test was designed to identify those students and to get them the help they needed. I believe that failing the test did not jeopardize one’s chances of continuing to study at the university, nor of graduating.
My experience with applying came as a surprise to my wife, who is originally from the United States, and is a product of their school and university system. She did sit the SAT and went through the interviews and wrote the essays and had her high school experience gone over with a fine-tooth comb (and yes, she did do enough extracurriculars to get in). The fact that all I had to do was fill out a form, and authorize my high school to send my marks to the universities I applied to, was totally foreign to her.
And like many of her peers, she started university at age 17, after four years of high school–which, I suppose, gets back to my original question about OAC. She did well starting at that age; why couldn’t an Ontarian?
If I can add a little more opinion, I’d like to see Ontario universities follow the American model a little more, if they don’t already. I knew a few people in my day who either didn’t make it, ot barely squeaked in, because in addition to studying, they were also busy playing sports, or in the drama club, or in the orchestra or working on the newspaper or yearbook or just plain doing something else. That kind of experience produces, I believe, a more rounded person who is perhaps better prepared for university life and life in general than one who does nothing but study. And I knew enough of those.
Just my opinion. Your mileage may vary.