I use the 70-200 f2.8l non-IS on my 7D, 600D and M, great results, nice range, only use in MF mode obviously, couple of bug bears however..
The lens will not sit nice on a video tripod plate, always seems to work loose: moral -don't carry camera on tripod between shots.
The lens does not stay in focus as you zoom.
I tend to use live view preview to focus check, but obviously this doens't work during record. If you change your zoom setting you are going to need to change your focus position slightly.
The older canon push pull zooms (70-210 f4, 80-200 f2.8L) do hold focus through the zoom, af can be very slow, but for video and on an adapted gh, thats hardly an issue.