Done a few 3D tests in the Victorian style using a couple of compact cameras that can shoot video. You may have to build a little dual tripod mount from a little plank of wood and a couple of screws, but essentially you mount the cameras no more than four inches apart and shoot your video. Then, in a suitable editing programme, you record your images as a split screen and you view them, close up with a card viewer. The idea of the card viewer is to mask what your left eye can see from your right eye, using a slat of card that projects from between the eye-holes. It's not avatar, but it looks lovely on a small scale.
There are a few beamsplitter rigs floating around on the internet that are being made for DSLRs (the GH1/2 specifically) but there are a lot of other problems involved in using a 7D to shoot anything professional in 3D like lack of genlock, differences in lenses, etc. Technically, its possible, but I wouldnt say it'd be an effecient way to shoot 3D. Also, convergence would be very difficult and not being able to focus on anything under 30 because of the interocular would be a nightmere.. For the price (2 7D's, a beam splitter, identical lenses, etc) you might want to spend a bit more and get the Panasonic AG3DA1. It's a sweet camera for run and gun 3D, and probably the best solution out on the market right now.