Erik,
you are actually asking about a number of different programs. I will try to respond to the different issues you have raised.
You are considering joining the Reserves once you meet the eligibility requirement while you are still in high school. You may want to read through threads of interest in the Recruiting Forum for a better understanding of the recruiting process and possible issues you may meet:
Recruiting FAAQ -
http://army.ca/forums/index.php/topic,17073.0.htmlJoining the Reserves as a soldier while in High School is a good way to get an introduction to the military. Many Reserve units do run Basic Military Qualification (BMQ) training on weekends through the school year, and you can attend other training course during the summers.
Once you get to the senior year of high school, if your intentions are to attend RMC, then your military career path will be changing significantly. Officer candidates at RMC are members of the Regular Force (not the Reserves). You will have to return to the Recruiting centre and repeat the Recruiting process as an applicant for the Regular Force. Keep in mind that being a serving Reserve soldier does not speed up this process, if anything it can slow the process because of the requirements for a Component Transfer. See the Recruiting FAQ links on Component Transfers and on Officers for more information to start your research with. Be prepared to start your application for the transfer and consideration or RMC very early in your senior year, to allow the Recruiting System to complete the steps it must put your file through.
Remember that your Reserve service will not be a significant factor for your selection as a candidate for officer training and attendance at RMC to the point where other perceived deficiencies would be waived. Your scholastic abilities and your general presentation as a well-rounded citizen with leadership potential and a variety of personal and inter-personal skills will be more important. No matter how much you may enjoy and wish to dedicate time and energy to your Reserve service, don't let these other factors slip to the point where they might undermine your application.
Good luck with your plans.