We're shooting Nikon rather than Canon, but both my wife and I carry two cameras with lenses mounted on most shoots. Yeah, one is technically a "backup," but along the lines of your thinking we might as well use it since it's there. We keep our most-used lens on our prime body, with the next most useful on the backup. That saves lens changes when speed is needed, as reflected in a decision about which lens we are most likely to change to when we need a change.
That all requires a survey of your images to determine which lens you use most, and which is next in line. It turns out that we use a medium zoom about 75% of the time, followed by a wide zoom at 20% and a long zoom at 5%. Yours selection might well be different based on localle and subject matter.
On the practical side, carrying two bodies simultaneously with lenses mounted can be problematic. We have found it best to use camera straps that are longer than fashionable today, so that the cameras hang down near waist level with our head and one arm through the strap. That lets us sling one over each shoulder so they are well clear of each other. We're using long straps from Tamrac, but I'm betting other companies have them too if you have a brand you're loyal to.
The long straps also make it easy to sling the extra around behind your back when a little extra elbow room is needed. We're often shooting with strobes mounted on each camera, so the elbow room issue is more than theoretical. Another consideration is the size of your camera bag. A big bag causes jockeying, and frankly neither of us like most of what's available on the market today.
For years we have used belt pouches rather than camera bags in our work, and in leisure times when wearing a daypack while hiking or shooting landscape. One of my consuming hobbies is leatherwork, and last summer I made us each a soft leather shoulder bag just large enough for one lens and a strobe, plus spare batteries and cards. They conform well to our bodies and because they also hang to waist level with head and arm through the straps, it's easy sling them around behind our backs and out of the way. Since we're both carrying those bags more and the waist pouches less, it's promising for the concept.
More than you asked for, but hey. It's early and I get chatty with my first cup of coffee.