I only had one interview, so I can't vouch for them all. It started with "why do you want to be in the Canadian Forces?" I replied with the usual; "I want to serve my country, Sir," "I'm hoping to go overseas and help people, Sir."
After a few minutes I was met with "no, why do YOU want to be in the Forces?" I was brutally honest and mentioned the reasonable pay and job security that you won't find anywhere else.
Try to look sharp. I just dressed business casual; slacks and a dress shirt, no tie. I was also told that I was the first candidate with a decent haircut in some time. Try to look professional. It might sound shallow, but I wouldn't hire some of the guys unless they gave a heck of an interview.
Any update from the OP? My interview was a while ago now, so things may have changed a bit. It sounds like they're getting tougher.