I would use the P2 unless you are good with manual focus which in necessary with the Canon. The lens and DOF isn't as awesome as it can be with the 5d, but the P2 is a legit pro camcorder that takes really nice video. The p2 files are easy to edit and deal with in Premiere or FCP. other reasons to use the P2:

On board stereo mic
Audio monitoring
XLR audio outputs
in camera ND filters
Tilt/swivel LCD screen

The Canon:

Light sensitivity
lens selection
Mass
Bigger sensor = short depth of field

-M