According to CATO 42-01 you need to be NSCE qualified and have passed any WO qualifying course, ie: CLI. Also, you have to have reached the age of 17 by August 1st of the training year and not 18 by the end of the course. You also need to be recommended by your CO in conjuction with your Corps‘ sponsor. Also, you‘ll need to pass a medical administered by a CF doctor, and finally, pass the your region‘s PT test to be considered. Generally, there are more cadets that pass than there are spots, so there is usually a waiting list of candidates. If you‘re really interested in getting on this course, talk to your unit CO AND Admin Officer to make sure you make all the deadlines for paperwork, physicals, tests etc. Then start training - I can‘t stress enough how important physical fitness is to passing this course!
Good luck!