I for my part think that Canon made the switch to a new process with the 70D sensor. Canon admited, that 18MP was the limit with the process they had then. So if they now make an APS-C sensor with 40million photodiodes (there are two diodes that can be read seperatly in every of the 20.2MP), then I think they definitly made the move to a new process.
For those who think that Canon has a problem with high ISO noise, just go over to DXO Mark and check the graphs (not their rubbish ratings, but the real measurments). Take the Nikon D600, Canon 6D and Sony a900; look at the graph, and tell me which camera you would take for low light photography. I think we have a clear winner with the 6D. The 6D looses out in dynamic range at low ISO, and has worse color sensitivity, but DR and SNR are better than the rest at high ISO.
Don't get yourself fooled by the DXOMark Rating, it shows not the whole picture. It is also difficult to judge what a 5 or 10 point difference means exactly.
I'm looking forward to the DXOMark measurments of the 70D; I think we will see some surprises, not that the 70D will storm to the top, but just a different behavior then the recent Canon sensor (which was rather predictable).