Dude, you don't have much time to figure this out and get your gear together.
Your camera will record 16-bit (48 kHz/2ch) PCM which is good enough, so I'd just add some external mics and record the sound on the video camera. What you need is a couple of decent mics and a way to get the signal into the camera. Buy or borrow a Canon MA-300 Microphone Adapter or a BeachTek DXA-4p. These will allow you to use mics with balanced outputs. However, they don't have phantom power, so you'll have to use mics that can be battery powered, or mics that don't need phantom power. Or you could get a BeachTek DXA-6A which has phantom power, but of course it is more expensive.
Now you need some mics. Rather than buying on such short notice, try to borrow some mics. Ideally, borrow some condenser mics that can be battery powered. Otherwise, borrow a couple of dynamic mics. Make sure they both are the same model. Get a mic stand and some cables and set the mics up in an XY configuration. Do some reading in the Microphone section for what I mean by XY and for tips on where to place the mics. Don't stress too much about mic placement if this is the first time you've made a recording with external mics; anything you do will probably sound much better than recording with the camera's built-in mics.
Forgive me for assuming you don't have much experience in audio. Keep it simple. Set up your gear and make some test recordings BEFORE the show. You'll learn a lot the first time. Good luck!