I have this:
http://www.amazon.co.uk/Lowepro-Fastpack-250-Backpack-Notebook/dp/B000YJ0O9...
It has good padded waist and shoulder straps.
The fast access camera pocket holds my 60D (previously 400D + battery grip = probably same size as 5D) with 120-400mm Sigma attached. I also fit a 60mm macro and 17-85 zoom + large flash. There are velcro repositionable dividers.
The top section has room for 4 field guide + 2 binoculars, or more usually lunch + binoculars + couple of guides + first aid kit + map + tools.
There are two handy card holders and a battery (or knife) slot on the should strap. The small outer pocket is big enough for charger + batteries. There is a mesh holder that fits a water bottle and a zip to put a laptop in the back - but I use it to secure my monopod.
There is a larger 350 model. The newer "video" version has a pull over cover and tripod straps - but I don't know if the internal space is as open.
I've been looking for a better holdall as the one limiting factor for me is that if I don't have the 120-400 on the body then the only place to store it is the top section. But I haven't found any other bag that would offer this improvement and no loss of other features.