PrimativeProfessor: "*Is this possible?"
No.
If you want a better time day-tripping whitewater in a solo boat, there are lots of good options. If you want to haul 800# of stuff on flat water, there are also lots of good options. No canoe expert is going to tell you that one canoe that can do both of these things reasonably well. If you're soloing class III in a Penobscot, it really doesn't matter what you build, YOU will get it where you're going.
2 canoes > 1 canoe. If I was selling you canoes out of my current livery, I'd suggest my Mad River Explorer for the solo and downriver work, and my 18'6" Wenonah Odyssey for the bigger trips where portages are more of a concern than rocks. With plenty of weight in the front you could probably handle the Odyssey on flat water reasonably well alone, but it is far from ideal. I'd never take a rocker-less kevlar boat like that down a river, however. If you wanted to bounce off of rocks with 800# of gear, well, you've got the Penobscot already. I doubt portage weight is much of a concern for a person your size.
Get out and test paddle a variety of canoes before you build one! Flat bottomed boats feel VERY different from V or shallow arch bottomed boats. Figure out what you like! The benefit of making one yourself is you can take a hull shape you really like and make it a little bigger, much like how the 38 Special came to be, IIRC it is simply a NW Merlin that was expanded 3.8% in every direction.
CALL around! Northwest Canoe is an excellent resource! Any mom and pop paddle shop is going to have valuable opinions. I foresee many people pushing you towards a Prospector, which has one of the best reputations for all-around performance and classic lines, but keep in mind that many companies have put the word Prospector on a canoe before, and they are not all the same.
Good luck, I hope you build many canoes!