The T3i is good, in general Canon models will give you a better "IQ" image quality and better selection of lens
(why the pros use Canon)
but also look for refurbished deals on T4i, T5i, T6i, etc.
Is the t3i a good camera ?
Yes it is but in its price range there are much better and more modern cameras like the Nikon D3300 that I mentioned.
Pro's use Canon ?
Some do, in my area I know more then few pro's and most use Nikons mostly the D610, D750 and D800/D810
The few that use Canon have 6D and 5D III
Stating pro's use Canon is very misleading, yes pro's use Canon and Nikon and lately I see some that even use Fuji and more then few are starting to o with Sony especially the A7R II
In regards to lens selection both Canon and Nikon have a big lens selection, unless you have a specific lens you like from a specific maker there is no big advantage or disadvantage with either Nikon or Canon with their lens selection.
And about looking for refurbished T4i, T5i, these camera use same sensor as the t3i and even the very old t2i, all use the 6 years old 18MP sensor
The t6i is a new camera with a good sensor, if you find one in your price range then its a camera to consider but I think its way out of your price range.
I still think in your price range the Nikon D3300 is your best choice!
As I said it will have better low light performance and much better dynamic range then the t3i