The curve is probably going to be the median grade in the class, but it could be the average. It will probably work out about the same either way, so I wouldn't sweat that detail too much unless you have a scholarship riding on it.
Yeah, this seems like a pretty normal grading system and a B- curve seems to be common. Also the attrition rate, as far as T4s go, actually isn't too bad. You make it past the first year and it looks like you're cool, so that's good. What were your numbers like?