Been backpacking 18 years. I have always gone very high carb diet out there. Now I am looking to go out on a lower carb diet? Where do I begin? What do you say, what do you do?

You will get a lot of opinions on this question. It depends a lot on what you consider a low-carb diet for a canoeing trip. It also will depend highly on the route and your level of exertion. A balanced diet approach with a "stash" of emergency healthy whole-grain carbs among your food supply would be a good precaution. I'll let others add more to this discussion.

Proteins are low in calories, so you will need fats to carry you. Like 25/25/50 or so for calories.

Nuts, low glycemic carbs like dried cherries without added sugar, ova-easy eggs (they may still sell the smaller size on their website). Tuna (in oil) or chicken foil packets, #10 can mountain house freeze dried chicken/beef repackaged, salami, hard cheeses, dehydrated vegetables with olive oil, plain oatmeal with oat bran added for fiber, Epic bars, Rx bars. Noodles have a relatively low glycemic index, just limit quantity to a tiny bit. Catch some fish.