You can get fairly lightweight touring bikes. Mine is an aluminum Devinci. Unloaded, it's light and responsive, but it can carry a fairly heavy load without problems. Devinci is a Canadian company from Quebec. Considering the value of the Canadian dollar against the U.S. dollar, you should be able to get a good price for a well-built bike.

Don't try to switch to a carbon fibre fork. You'll get some weight savings but the difference will hardly be worth the price you pay for the switch. You'd be much better off sticking with the stock frame and keeping your gear load light.

On another note, I'd personally be hesitant to carry the gear in a backpack. Even if you keep it light, your back will hate you within a couple of days. You're much better off with a rack and panniers. This keeps the weight low and more importantly, it keeps your back happy. Backpacks work well when hiking but on the bike, you're in a different position.