Hope this bit of info can help!
Know the training (where, on what, how long, etc...). Also know what a pilot in the CF does (flight safety officer, secondary duties, desk tours, etc...). Know the aircraft the CF has, perhaps a few it recently lost, and those it may be and will be procuring. It would be a good idea to know a little bit about flying at least to show you have alot of interest, From The Ground Up (FTGU) is the perfect book for that. So basically know the life and roles you may have to have right from when you start training untill they day you retire. I would think as well it wouldn't hurt to know a little bit about the trades that directly support you (FE, AVN TECH, AVS TECH, ACS TECH, SAR TECH, Air Nav, etc...), but perhaps only a what they do and how you and them will work as a collective team to accomplish a mission.
Overall take it easy, go in there with the attitude that the interviewer just wants to talk to you and see what you know and how interessted you are, he's there to help you not to try and make you fail. Try not to be nervous, you can't get nervous in the air when a crew's life rides on your decisions.
Good Luck!
R.