GH3 & 100/300 or Canon 7D 100-400L

You'll also want to get the micro-focus adjusted to match the lens with your 7D.  The 7D only allows one adjustment per lens so have it adjusted at the focal length you will use the most.  Hopefully the rest of the focal range won't be far off.

This is one of the reasons I am hesitant going back to PDAF, as CDAF doesn't require focus adjustments.  I am also used to all the advantages of an EVF.