Have you adjusted the audio level up in the camera menus? If not, try that. Also, there might be a switch to go between the built-in and external mic, although, it's probably a mechanical switch in the mic-in connector. Here's a link to the page with the camera instruction manual.
http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&fcategoryid=1...
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24" TV-Logic Monitor
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5
Final Cut Studio 2 (up to date)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN
