Hi there,
I got accepted into Co-Op for Computer Science last year. Like brent012 said above, you can't do a double degree in Co-op. However, it *is* possible to do a double degree in later years - you have to get permission from sponsors and also your faculty to transfer into a double. (edit: you probably have a better chance of getting the double accepted if the extra degree is relevant to your program. e.g. a mathematics/computer science combination would probably go down a lot better than an arts/computer science.)
Advice for getting accepted - first, don't leave the application until the last minute. There are a lot of questions and it's very tedious to fill out the form
P). Also perhaps get someone to review your responses, make sure they're coherent and such. Other advice - it looks really good if you've well-rounded, e.g. have done leadership activities or such. It's a bit hard in year 12, but extracurricular achievements/activities help your application a lot. Especially if they're relevant to the discipline you're applying for - having those extra experiences to talk about helps in the interview.
If you get into the interview, you're going to need to be able to talk to two interviewers (at least, there were two people who interviewed me) and coherently discuss some of your responses in the application form. So, you'll need to be familiar with what you wrote on the application form. And also, don't forget to keep eye contact, appear confident and so on. (Even if you don't feel confident, act it! Looks good.) (heh my interviewers didn't know each other so they were a bit awkward after I finished answering a question - they looked at each other as if they expected the other to ask the next question)
What's it like doing the Co-op for my course? Well, there've been a number of events with my co-op cohort and they've been fun. I haven't gone on placement yet and won't until second year, so I can't speak for that part of the scholarship. But meeting other people at the events is great
Anyway, I hope I helped somehow.