While looking through the setup menus for the 100th time I found an Autofocus setting that can be applied while you are shooting video. Normally I set the lens on manual, but it is not necessary when shooting video with the 5D, the normal AF is turned off automatically.
Now I don’t recommend this as a way to focus, but it is interesting to know that the function is in there. I think the best resource for accurate focus is the regular viewfinder, followed by Zacuto Z-Finder. If you get one, I actually prefer the snap on attachment over the bracket and mounting plate that comes with the Z-Finder Pro.
But I found this setting under Wrench 2 Dots > Live View/Movie func. set. > AF mode. You have 3 choices, Quick mode, Live mode, and Live ‘L’ mode. If you set it to Live mode the camera will do a rudimentary auto focus for you. This video explains how: