Actually, Nikon has supposedly caught up and surpassed Canon in high ISO performance. Note the D3 uses a FF CMOS sensor designed by NIKON (NOT Sony) engineers. From
http://www.imaging-resource.com/NEWS/1187901361.html:
"The D3's high ISO is really impressive I'll remain at least somewhat skeptical until we can get a D3 back in the lab and test it under controlled conditions, but Nikon showed some incredibly impressive prints at the event. They had enlargements that must have been 30x45 inches or more in size, comparing identical shots taken with the D3 and Canon EOS-1D Mark III at ISO 3,200 and 6,400.
After the disappointment of the D2H, I have to say I was taking Nikon's claims of low noise at high ISOs with a rather large grain of salt. When I saw the aforementioned prints though, I was literally flabbergasted. The D3 didn't just surpass the 1D Mark III, it far surpassed it. Well, that may be a little strong; the Mark III is a fantastic camera, but the difference between its images and those from the D3 was anything but subtle. As I say, I'll remain a skeptic until we can test a production sample of the D3 ourselves, but if the images shown had any basis in reality (and Nikon would be foolish to have doctored them in any way), it looks like there's a new leader in the high-ISO / low-noise derby, and it's the D3."