My "new" camera system. Two Olympus E-P5 bodies and Olympus lenses: 12mm f2, 25mm f1.8, 45mm f1.8 and 75mm f1.8. Also a small Olympus flash.
I've used Canon cameras for as long as I've been a photographer. The first camera I used was a Canon FT-QL, a tank of a camera. The QL stood for "quick load," a Canon innovation that made it easier to load a new roll of film into the camera. We got that FT-QL at the PX in Bangkok in 1967 or so.
Even then, Canon and Nikon were the big two of the camera companies. The others, Minolta, Olympus, Ricoh, Yashica, etc were playing catch up to the CanNik juggernaut. Leica was always in a league of its own.
Through the years I've flirted with other systems.
In the 1980s, one paper I worked at issued me Olympus OM bodies and lenses. The lenses were excellent and the bodies nice and small, but I stayed with Canon for my personal gear. In the late 1980s, another paper I worked for issued me Nikon gear, FM2 bodies and a selection of Nikon lenses. They were okay but (and this might be heresy to Nikon fans) they didn't offer me anything the Canons didn't, so I stayed with Canon. (Although I have to admit the Nikon FM2/FE2 are arguably the best looking 35mm SLRs ever made. Nikon nailed the aesthetics of those.) While the Olympus gear was substantially lighter than my Canon gear, the Nikon gear weighed about the same.