"Rejoice oh young man in thy youth"
In other words....make sure your grades are above reproach, ensure that you parlez francais, and study study study. RMC is one of the hardest to be "accepted to" of Canada's Universities.
The second bit of advice I'll give you always have a back-up plan.
Reason being I started out much the same as you are in right now. Followed the "natural" order of things Cadets, Reserve, Applied to RMC (turned down) Applied as a foreign student to the Military Academy at West Point (Accepted - Turned down by the Canadian Government for referral) Regular Force. Out of my circle of friends at the time 20 of us applied to RMC and Royal Roads and 3 were accepted. I joined the Regular Force after post secondary at 23. At 27 I was injured during a training excercise in preparation for a tour overseas. I fractured my lumbar spine in four areas. Two years later at 29 it was finally diagnosed and could not be operated on (I had too much mobility to gain anymore from surgery). At 30 I was processed and medically released from service my career ended.
My fall back position was that I had continued with my pursuit of education while still in. I fell back to working in Law. I now work as a Paralegal, defending people in Small Claims, Provincial Offences, and Family Courts.
I hope you will be successful in your pursuits. You will never find a closer bunch than any branch of the military. Land, Sea or Air it's all family.
Cheers;
Gregory