Hi there Jenaya!
I have kayaked at 200 or so pounds, in Massachusetts lakes and once around the Seattle bays. The openings on most kayaks are pretty wide, so no squishing, and they should be able to hold your weight certainly. They are sturdy and quite bouyant. It can be a challenge to get IN them as they tend to move around on the water, but if you hold onto the tie-down or dock and the kayak edge (squeezed together with one hand) as you get in, it's easier. It gets smoother with practice
If someone can stand by and hold it still for you, even better.
I'd start off with a small time, like 30 minutes? Depends on what you do right now for exercise. Kayaking is a big upper body workout, and a bit of legs too, with the steering pedals inside.
The motion of moving the paddle through the air and water takes a bit of practice too heh! Kinda like patting your head and rubbing your stomach... to get it down where you are not wasting a ton of energy and moving yourself smoothly through the water. Not as hard as sculling though - phew! Sculling is a major balancing act. Very Zen.
Canoeing is fun too... I'd venture to say more leisurely than kayaking usually.
A bit of reassurance: once you are IN a kayak, it is really hard to dump yourself out. Unless you are in white water rapids or something extreme sports-like
Because they are shorter and squatter than canoes, they can take a lot of motion before something dramatic occurs
Wear a life jacket too, just in case... even if you can swim well, it makes it easier to tow yourself and the boat back in if you are not busting your butt to stay above water
Give it a try... I'd love to hear how you like it!