this is doubtful. canon has their hands full with refreshing their aps-c line, keeping up with the C line, and figuring out mirrorless. they are doing too many things at once.
2013 may see a 1Dsmk4 the earliest. Full frames are done for 2012 as far as canon goes.
Don't underestimate the power of market forces. I'm sure Canon has had a high MP sensor in development for quite some time now, don't be fooled into thinking they were caught off guard by the D800, I'm sure they knew what Nikon was going to release, but I also think they were caught off guard by it's price point.
As stated, the million dollar question is if Canon has found a way to compete with the admittedly excellent low ISO DR of the exmor sensors. I don't subscribe to the D800 hype as I need a more well rounded camera, but once Canon releases their high MP body, landscape photogs WILL want the ability to push shadows like the Nikon competition. Sony has set the standard for low ISO DR performance and Canon would be foolish to release a camera that's not competitive in that regard. The camera would also need to be better than the Nikon at ISO 6400+, I would expect a decent 12,800 but not much better due to the huge pixel density.
I've never really considered the 5DIII & D800 to be direct competitors, they're very different cameras.
I believe development of this high MP camera is already well underway, and a 2012 announcement with an early 2013 ship date is very probable, but I'll say get ready for sticker shock. You just aren't going to get a uber MP body from Canon for $3K, I fully expect it to be in the $4.5 - $5.5K price range. For that price, I would reasonably expect the 5DIIIs 61pt af, dual CF slots, dual digic V. I would also expect it to be able to shoot the same 6 fps as the 5DIII, if a single Digic V can push 22MP files at 6fps, there's no reason that dual digic Vs couldn't do the same with 40MP files, although Canon just can't skimp on the buffer like they did with the 5DIII.