LOL ! go to a Canon forum and see all the former Sony users! (and Nikon!)
Or join a local photo club where everyone is shooting the same subject and same conditions then compare the pics (bring some memory cards!)
There's a reason most pros use Canon !
And check the Sony or Pentax or Nikon forums, and you will find people who abandoned Canon as well. Plenty of flipping fan boys.
Plenty of reasons many pros use Canon (and many also use Nikon), the biggest of which is lens availability and software compatibility.
And remember, pros who invest heavily in lenses, don't switch overnight. In the 1990s to earl 2000's... Canon was supreme and the best. Pros went to Canon in droves. In recent years, Canon's image quality as been surpassed, but little differences in IQ isn't going to get a professional to dump thousands of dollars in lenses.
And the IQ of the top Canon fullframes is something...
But in terms of the consumer grade crop cameras...
DXOMark is the trusted source in rating image quality objectively.
So DXOMark scores:
Canon t3i: 65
Canon t4i: 62 (yes a small step backwards)
Sony A57: 75
Nikon D3200: 79
Pentax K-30: 81
As you can see, it's not really even close. In terms of solely image quality, Canon can't match the current sensors being used by Sony, Nikon and Pentax. But in 99.99% of situations, you won't notice a difference.
Again, these are the consumer grade cameras...
Moving to the the semi-pro fullframe cameras:
Canon 5d Mark iii -- IQ of 81
Nikon D800 -- IQ of 95
Sony A99 -- IQ of 89.