I'm actually just finishing my first year as a high school teacher, so I can weigh in on this a bit. When it comes to teachable subjects, in general, it's like this: if you want to teach high school, you'll want to specialize in 2 subject areas (that are considered "teachables" by the Ministry of Education). If you want to teach elementary school, you *want* to be a generalist - that is, you want to have courses spread out over a wide range of subjects. That's because, as Sarah mentioned, elementary school teachers are responsible for teaching a wide range of subjects.
First off, let's get the technical names for the teaching divisions out of the way:
-Primary/Junior (P/J) = Grades K-6
-Junior/Intermediate (J/I) = Grades 4-10
-Intermediate/Senior (I/S) = Grades 7-12
As a practical matter, if you get qualified in the P/J or J/I division, you'll be teaching in an elementary/middle school (despite J/I technically going to grade 10, teachers with this qualification virtually never start in high school). Getting I/S typically means you'll be teaching in high school (despite, again, technically going down to grade 7 - although getting job offers in the senior elementary panel with an I/S qualification is possible, especially if you're male).
Admission requirements get a LOT more specific than what I mentioned earlier, and vary somewhat from school to school. I went to Western for teacher's college, for example, and for their I/S division, the entry requirements were typical: 5 full courses in your 1st teachable, and 3 full courses in your 2nd (where a "full course" is defined as one that lasts a full year - Mac doesn't have many of those, so the equivalent would be 10 3-unit courses for your 1st, and 6 3-unit courses for your 2nd...confused yet? :p) If you wanted J/I, then you'd only need one teachable, with 4 full courses in that subject, as well as some other various subjects as well. And if you wanted P/J, you'd need a smattering of courses from many subject areas.
A good starting point for Western is this page, which breaks it down by division:
http://www.edu.uwo.ca/preservice/interested.html
But again, all the schools are a little different.
As for whether or not SocSci will prepare you adequately for teacher's college, I think that if you're heading towards teaching in elementary schools, then it's pretty much the ideal program. It'll allow you to get the diverse range of courses that are needed to get into P/J or J/I programs most easily. If you have a change of heart and decide you want to try for high schools, then it'd also allow the needed specialization (in subjects like history, geography, etc.).
Now...I'm somewhat reluctant to mention this, because I truly don't want to sound discouraging, but there's something that you have to consider...the job market for teachers at the moment is absolutely dismal. It is very, very difficult to get a permanent job nowadays because the big wave of baby boomer retirements has passed, and there are a lot of young teachers that came into the profession over the past 5 years or so who took those job openings. Even so, the Ontario teacher's colleges (and the border schools in NY and Michigan) keep cranking out more and more teachers without much regard to how many jobs are actually available for them when they graduate. I still don't have a permanent contract position - I've been given what are called LTO assignments, which stands for Long-Term Occasional; that means that I fill in for teachers on long-term absences (like maternity leaves) at various schools. I know others who have been doing similar placements for the past 3 years, with no end in sight. It's real teaching (as opposed to supply teaching, which is more like babysitting...) but it's unpredictable, and not necessarily steady work. I've been lucky to have been on 2 almost semester-long LTOs this year (with supply work in between), but other people I know have either barely worked, or didn't get on the supply list at all. If you persevere, and "pay your dues", so to speak, then eventually you'll be rewarded with a job; alternately, you could get very lucky and get a permanent contract right away, but it's rare. It also increases your chances if your teachables are in a more "in-demand" subject (such as elementary French), or you're willing to move to a more underserved area (which, sadly, excludes pretty much all of Southern Ontario).
I don't say that to disillusion you - if you know you want to be a teacher, you'll follow your heart, and eventually it'll pay off. Perhaps part of me put that up there to dissuade people who may be reading this who think teaching's "easy money" and they're guaranteed work - you're not, and trust me, you'll never have worked harder in your life when you're first starting out. You have a long time at Mac ahead of you, and you may well find something else you absolutely love in the next 4 years and change course on your future plans, which is just fine. If you know you want to teach, though, kudos to you, and just make sure you educate yourself on both the mechanics of getting into teacher's college and what to expect after you graduate. Demographics can certainly shift in 5 years' time, so who knows, your particular subject or area may be a hot commodity at that particular instant.
In any case, good luck with it, and if you have any other specific questions, I'd be happy to help!
