I downloaded 3200 ISO raw images from http://www.imaging-resource.com/ for both the Sony Alpha 900 and the Canon 5DII. I converted both to TIFF using "DCRAW" http://www.cybercom.net/~dcoffin/dcraw/
I would be cautious with that, for
1. ACR does not handle the A900 files properly; I don't know how dcraw is doing that, nor do I know how exactly they should be treated.
2. The Sony A700 does carry out NR
on the raw data; I don't think the A900 is different. In an earlier firmware version of the A700 this was not switchable; now it is, but I don't know if the file you are using was created with NR OFF.
3. Your
Canon has a tighter noise pattern is quite an understatement; the A900 image is
blotchy. This may come from the incorrect interpretation of the raw data, or from a botched noise reduction (already in-camera), or from the combination. It is unacceptable in my eyes, as it is now, but I am not sure if it can't be made much better with another raw processor. That time, when I was dealing with the A700's blotchiness, I was told that Sony's raw converter yields better result (but its workflow was not as good as ACR). It is possible, that the A900 image would look much better with Sony's converter. The ineptitude of some raw converters can not be held against a camera.