I own a Canon 7D. Admittedly, I am a waaaay better photographer than videographer (which probably isn't saying much), but I would NOT buy a DSLR for action video unless you already know what you are doing and have a dedicated camera-person who knows what they are doing (angles, lighting, settings, pulling focus, etc).
I take my 7D out on the slopes and while the pictures are GREAT... the few videos I take always come back sucking. A big part of the problem is trying to keep the action framed with one had, pull focus with the other hand while trying to keep my body/snowboard relatively still.
My friends with ultracompact cameras and cell phones (well, the Galaxy Nexus, which is no slouch) usually get more useable video clips than I do.
Between the 5D MK 2 or 7D, go with the 7D because it can use less expensive crop sensor lenses and because the auto-focus system on it is newer and better than the 5D Mk2.
I would strongly consider a 60D and spending the money you save on hand-held, 1080p video cameras or even RC choppers for mounting POV cams.
Wetstuff is right. Pro gear won't give you pro results without pro-know-how. Go with mid-range gear until you get good enough to bump up against the limitations of the hardware.