"I'm still not sure exactly what happened, but it was alarming."

I'll speculate a bit - the wind "shook" or "shoved" the canoe and you tensed up, which is a natural reaction to an unexpected shove - if so, that is absolutely the wrong thing to do.  Any canoe should be able to handle being sideways to wind and waves, even big wind and big waves, especially if you are prepared for a quick brace with your paddle.  Tensing up, when the canoe leaned downwind, your body leaned also, and being top heavy, over you went.  In cross wind/cross waves you need to be flexing at the hips, keeping your upper body/torso upright and between the rails, and letting your lower body rock with the canoe - so your hips and the boat will be rocking with the contour of the waves and wind, but your upper body stays upright, within the rails.

I do an "exersize" the first time i climb into my very tippy whitewater boat - as soon as I'm setteld in, I go and rock the boat rail to rail, or at least a lot, while maintianing an erect upper body, letting my lower body rock with the boat  (flex at the hips) - after about 15 seconds of that, my boat no longer feels tippy - I'm "tuned in" to the boat, and staying upright becomes a more natural reaction.  Sometimes, I'll do that in my other solo boats - maybe right after leaving the dock at Nym L.  Not to say that I still don't get ejected from time to time.

so next time you get into an unfamiliar boat, give that exersize a try - it'll help settle you in.

I've gone down rapids and big wave trains frontwards, backwards and sideways - the boat will get through anything just fine, unless I screw it up.  Same thing in lakes in big wind and waves - a boat won't go over unless you tip it over.  Stay loose.