I've been searching for something similar but then for traveling within europe.
The max carryon weight in europe is also 7kg for several airliners nowadays.
I've been searching for a bag with maximal dimensions: 50cm x 32cm x 20cm (19.5"x12"x7.5"). Also the bag should be very light.
Up till now I only found the following backpack that comes close to my demands:

Eagle Creek Mountain Valley backpack
http://shop.eaglecreek.com/mountain-...ackpack/d/1243

Did not buy it yet though, but reviews are good. Maybe this is also something for you.
Btw I think 32 liters (about 1950cu) is more than adequite for serveral weeks of traveling.
I like to travel light