i own and use both a 5D3 and 7D. This pairing replaced a 5D and 40D. The 7D is used principally with my 100-400 and 300 f/2.8 (with and without TCs) for sports photography. Very often, the 100-400 will be on the 7D and a 70-200 on the 5D3. With the focusing improvement, the 5D3 is a passable sports camera, something the 5D never was.
However, I have also used a (1) 17-35 on the 5D/5D3 and 24-70 on the 40D/7D, (2) 24-70 on the 40D/7D and 100-400 on the 5D3 and (3) 17-50 on the 40D/7D and 70-200 on the 5D/5D3.
Having said that, if I were regularly shooting events and/or weddings, I would certainly buy another 5D3 and relegate the 7D to backup status.
Regarding the mythical 7D2, I want improvements in DR and high ISO image quality over the 7D, not more pixels. That's what I said about the 5D3 over the 5D2 and that's what Canon delivered.