Does the Sony SLT A35 outperform the Nikon D3100 / Canon 1100D?
On Image quality.manual settings (selecting aperture, shutter speed, ISO, etc) . And low light performance?
Each of the cameras you mentioned have their pros and cons, and I can't pick one and say it's the best.
The Nikon has the edge for low light, high ISO stills. But it has no autofocus motor. Not all Nikon lenses have motors, it's a major pain. All the entry level Nikon bodies lack the AF motor. The Canon does not have this problem, and it also seems to be a better video shooter over the Nikon.
The Sony is the only one with fast phase auto focus for video (if you want it, you can shoot manual focus if you want) Canon and Nikon dSLRs do not have fast phase focus for shooting video, regardless of price or model.
Also, the Sony has an anti shake sensor. Canon and Nikon do it in the lens, and only some lenses are anti shake. So with Sony, everything is stable including all the prime lenses, Canon and Nikon don't have stable primes.
As far as manual settings, well every dSLR has those controls from Sony alpha to Pentax, so not sure what to tell you there. Forced between only the bodies you mention, I would go Canon or Sony, the AF motor thing with the Nikons is annoying. To get around it, you'd have to step up to a mid range Nikon, like the d90 or D7000. If you planned on shooting a lot of video of fast moving subjects, the Sony wins hands down it has the fastest auto focus when shooting video, and it can shoot more frames per second for stills.
Let's just say for the heck of it, that we went up the chain, to camera bodies that were 1000 bucks or so, then Canon falls off the list because the sensors don't get any better, even if you spend 1800 for the Canon 7D. Then it would only be a Sony and Nikon race, thinking the Nikon D7000, Sony A65, or A580.
Haha I have experience using two from the three which is the sony and canon. The canon is complete rubbish to me. In terms of still photos both are the same but the difference is in the movie mode. Sony has fast af, full hd, and multi frame noise reduction. It got creative filters and a lot more toys too like 7fps burst with af. Between the three i will choose the sony. The only fault i found on mine is the mic is bad. And thats it probably