I just shot a video today with my GH2 and a 7D. The 7D has a 1.6 crop and GH2 has a 2.0 crop factor, with the difference in light that the sensors capture should i have used different ISO's on each camera?
There are many things besides ISO that affect exposure on a camera. Simply shoot properly exposed video with both with whatever settings that is for each.
Shoot the flatest possible settings on both and try to match them in post is what I would say. You'll probably have to up the contrast on the 7D in post slightly. White balance for whatever would get you the whitest on both cameras...