Over the years I've used a variety of film and digital cameras and lenses from almost every manufacturer you can think of (and probably some you've never heard of). Excluding my lengthy list of film cameras, if I focus on just professional digital cameras (DSLRs) I was exclusively a Nikon and Fuji DSLR user for roughly five years, then I switched to Canon for one year ... and then I switched to Pentax and I "might" stick with them.
That said, I also currently use Olympus, Panasonic, Leica, and Nikon point-and-shoot cameras when I'm not working in a professional capacity.
There's a lot to love and hate about every camera system on the market. Every DSLR system has its strengths and weaknesses. There's almost never just a single lens or single DSLR that can get the job done ... you can usually create the same types of images with cameras/lenses from different manufacturers. It all boils down to personal preference and shooting style.
Camera and lens manufacturers (and their ad agencies) want you to believe that the only way to get that perfect shot is if you use X camera or X lens. That's just complete nonsense. Yes, to some extent you may need certain features in order to get very specific shots in very specific ways, but the skill level of the photographer is MUCH more important than the choice of equipment.
It's ultimately up to the individual photographer to use the gear that he/she prefers. The only reason to stick with one particular DSLR system is so you don't have to spend huge amounts of money building a well-rounded kit for multiple lens mounts. My suggestion is to take your time researching (and going to camera stores to try out different cameras) before you make a choice.
Brand obsession/brand loyalty is for shutterbugs who need to believe that a bad camera is to blame for their bad photos. Photographers don't give a shit about the name printed on the gear they use ... they just need to know it's capable of helping them craft the image they want without getting in the way.