KPR,
I will say the following because I admire parents who take a great interest in their children's education. So please take what I have to say with a grain of salt.
1) There is a search function on the forum, located top right, which will give you the results of pages and pages of all things regarding RMC enrollment and criteria. In fact we have a thread dedicated to RMC and other military university and education programs located here:
http://forums.milnet.ca/forums/index.php/board,56.0.html
2) As stated above all things with regards to the Second Language (be that French or English) were hashed out countless of times, and could also be found using the SEARCH function. However, I will tell you this. Regardless of your French grades in HS or University, you will be sent to SLT, or to take a proficiency exam which will grade your fluency, competency, written and oral skills.
3) Now, grades are not the be all and end all anymore. We want well rounded applicants. Sure his PRes time MAY help, depending on how his leaders view him and the assessments passed forth. He needs to also demonstrate leadership in the community, have community involvement, academics and physical fitness. They are all important, and must all be thought about on how to achieve them in a balanced state in order to help him.
4) Lastly, he is now a soldier. Tell him to use his initiative and ask hi CoC. Better yet, tell him to go to the local CFRC and talk to the recruiters there, and if possible (during the summer some RMC students work at Recruiting Centres) talk to RMC students. INITIATIVE! It's important that he starts learning about that NOW. When he is deemed to be a successful officer candidate, he will have to demonstrate initiative and leadership potential everyday from that point forth. Mind as well start NOW.
I hope all the best to your son. I may have come across a little pointed, but this is the best way to answer your questions, and include you in our community. Next time, use the search function, and you will see what I mean by many things have been answered.
Best of luck. Maybe he won't want to RMC but other entry schemes.
MT.