Hi Welcome aboard
Have you been in a shop and handled either camera?
Have you got an existing lens collection?
What lenses are you looking at getting?
Have you considered the crop sensor versions like the 7D, why does it need to be a full frame sensor and then why not consider the 6D?
For Landscape, Portrait candid shots, the 6D seems like the better option than the 5D III.
ie you can buy a 7D and a 6D for the same money as the 5D III. Two bodies can offer a lot of flexibility.
The Nikon D600 seems to deliver a lot, why do you think you need the D800?
If I was looking at starting right now, I would seriously look at the Sony NEX system, purely for the smaller size.
Canon Powershot S95, Canon 6D,7D, Canon 40 2.8 STM, Tamron 24-70 2.8 VC, Canon 17-40 L, Canon 15-85, Canon 85 1.8, Sigma 30 1.4, 50mm 1.8, Canon 100 2.8L Macro, Canon 70-300L +Kenko 1.4 Pro 300DGX, Canon 430EX II and RS 4 Classic