Is it certain that the new 24-70II is going to be the kit lens for the 5D MkII successor?
No. There is no solid info on a 5D3, and there has been rumors of it for 2+ years. Which lens it will have as a kit lens is speculation on top of speculation, or people just really wanting it.
Kit lenses are rarely the best newest lens Canon has introduced. My guess is if the 5D3 is offered as a kit, it will include the 24-105mm f4 IS as it's kit lens. (I'm not saying this is what I hope happens, just what I think will happen)