Kayak for 300lb guy plus gear

Eddyline Denali?

https://eddyline.com/kayak-model/denali

I have one, nice roomy kayak

agree with magooch, for a full size boat the Isle is a really nice greenland style big boy boat. I have it in Kevlar, which is 50 pounds but it is 18 feet. If you’re going that length, the CD Titan feels much bigger inside (I thought uncomfortably so) and CD used to make a British style big boy boat that was very roomy (don’t remember name right now).

https://www.cdkayak.com/Kayaks.aspx?id=44

https://www.rapidmedia.com/adventurekayak/categories/boats/5251-boat-review-the-solstice-gt-titan-by-current-designs

Someone your size might want to consider a 2-man kayak like a Pamlico 14T and remove the extra seat and use it as a single seater. This is what i did for use as a fishing kayak.

Check out the Native Watercraft 14.5 Slayer. It is billed as a kayak with a 450 # capacity.
I have paddled one of their SOT and was impressed .