When I was younger, I solo-paddled a 17-foot Peter Pond canoe from Lake Itasca (the source of the Mississippi) some 2400 miles to New Orleans. I never rolled it, or even came close, despite some pretty hefty thunderstorms and the six-foot backwash from river towboats (and the fact that the canoe was considered fairly radically sleek for its time.) Controlling a canoe isn't hard, if you do a little training. I also took my two young kids and wife on some substantial trips in the Boundary Waters, without incident. My feeling is, that is the normal course of events. Rolling a canoe is a severe accident (unless you're deliberately courting it, by running whitewater.) An acquaintance of mine rolled a canoe right after ice-out in the Boundary Waters, and died of hypothermia; the general judgment of his friends and enemies alike was that what he'd been doing (using an antique side-mount motor) was stupid...
All of this to say that if you have sensitive equipment it's probably wise to waterproof it during travel, which can be done with a relatively inexpensive whitewater bag. Or, if you don't want to do that, some big Ziplocks can do the job, but don't last. But, don't be afraid to take the camera out, either, and without protection. Tell the kids to stop splashing around while you're shooting (my kids were as raucous as any, but they learned to pay attention in canoes -- a real necessity for safe travel.) If I were you, and on your budget, I'd buy a m4/3 camera and a couple of lenses, like the 14-45 and the 45-200, which would give you good high-quality shots in a compact kit, with the 35mm-equivalent reach of 28-400mm. (I never found ultra wides to be of that much use in a canoe. Your mileage may vary.)
Don't trust "stable" canoes. They can be treacherous. They will stay flat, flat, flat and then boom! they flip over. A "tippy" canoe with a rounder bottom profile can often be tipped (if you're kneeling in the bottom) until the rail almost touches the water, without going over.