@tsarstepan,
To get acclimated onto the modern SLR tech, be aware that most of todays lenses are "Steady cam" varieties and I highly endorse this because I do a lot of shooting from moving platforms.
Also, a good course at an ART SCHOOL (not a community college) will help. The Art SChool mentality will be teaching you the composure and creative stuff along with the workings of the camera.
A camera is just the tool of your craft of photography. A DSLR, because of its structure, allows you to just pile up photo after photo while giving you instantaneous results . You should then be spending time on the composure and the design and then shitcan the rest.
Good Luck.
PS, I would ask some professional photographers about their choices. I think that most police departments use NIKONS for evidentiary work. When I look at Nat Geo and Nature Photography, I see a huge amount of shots don on CANONs. Id ask some of those people , why do they use what they use.
One thing the CAnons allow , is to adapt your old lenses via special Xto Y adapters.(You can adapt even NIKON lenses to shoot on CANON camera bodies) I dont know if opther brands do that. Of course the newer steady lenses are a huge breakthrough in tech.
In summary, I think you will find all of us "loyal" to our brand. Over all, theres probably not any differences in the final photo product, maybe how you get there is what you should be asking about.
I like CANONs because they are so intuitive and all the buttons are right there.