A lot of guys on this board will complain that your question is too precise... but, eh, maybe someone CAN give you a precise figure.
My "limited experience with the CF advise" is that with the increase of current recruitment, I would suppose that getting into a ROTP would be easier than a few years ago... if you have good marks (like a 75%+ average) and have community/sports experience, you should be fine. Keep in shape, study well, and don't do drugs (some guy complained on this forum that the CF rejected him for doing pot only a few times).
If you are good enough of an applicant, it should be no problem. If you don't get ROTP, you can always re-apply next year for ROTP or apply as a DEO. Also, I don't think you would be disadvantaged by a recruit from say Ontario or Quebec.