Jay,
Like Retired_FDO said, I think your chances are not bad. Besides your school marks, what will make the balance tip is certainly your extra curricular activities, your volunteering being a big part of it. The track and field shows that you have some interest in physical fitness, also a plus. For the leadership aspect, your position as 2IC in cadets is certainly a good advantage over the competition. You should also seek other leadership opportunities. You need to remember that, for officers, the CF is looking for well balanced individuals able to function is stressful leadership positions, so you need to do everything in your power to show the recruiter your capacity to do just that...
RMC works with 4 pillars: academics, athletics, bilingualism and military... The best advice I can give you is to start learning the other official language, probably french in your case. Even though it is not a requirement for recruiting, it is a requirement to graduate from RMC, so the sooner you start, the easier it will be Also, it will be an advantage during promotion boards. For the selection process, having started a second language training of some sort shows you understand it's importance in the CF...
On a side note, use the fact that you were in a leadership position in Air Cadets all you want during the recruiting process but as soon as you step on your Basic training, never mention it. Surely use the knowledge you gained through Cadets as a tool to make
life easier but for the rest, let your instructor show you the ropes... basically the only difference between you and the next guy is that you know how to use a ironing board and how to shine your shoes. I was in cadets myself and never said a word about it... there's always a smarta** that tries to show off and ends up in trouble for some stupid reason. At the beginning, it will also make you stand out of the crowd and you don't want that, you want to be recognize for what you do, not what you should have done because you should know better because of your previous experience in Cadets...
Anyway, take it for what it is... just my :2c: