I flat water on lakes with a sit-on-top; I just use my normal carry at 3-4 o'clock with one of those newer style thinner life jackets. It doesn't really seem to affect me, and I typically don't remember I have it on. I suppose it depends on what you carry but my G40 with a light would fit the same holster.

Not sure if this meets your needs for a sit inside kayak... nor the hand cannon you want to carry but the "Stohlquist Fisherman Life Jacket" (the one with two large, semi-round zipper pockets on the front) fits an unholstered G26 size pistol quite well; draws much like a chest holster. This PDF also has the half-sized back panel so as to make it more comfortable when sitting in a kayak.

I’m carrying a much smaller pistol. I always have a Glock 42 in a vedder holster in my stohlquist fisherman pfd. It fits perfectly in one of the pockets.

If you’re set on using a chest holster, I’d suggest looking into ones that offer quick-release options or better access. I had the same issue with a chest holster when I started kayaking, and I found that some holsters have top flaps or quick-access designs that make it easier to get to your gun even with a life jacket on. Also, you might want to try different positions for the holster to see what works best for you while you’re in the kayak.