Now that I have a big back yard, I think I want to do some reseach on building wooden canoes. I would want a very light one.
2nd the recommendation on JEM.
then there is Pygmy:
If you have a big poplar or spruce,
drop it and do a dugout.
Cedar Strip boat?
They can be quite light.
For a little more work you can get a nicer shape with strip plank construction and to really keep the weight down try to get paulownia instead of the usual western red cedar. For light weight taken to extremes look at this one http://www.storerboatplans.com/Balsacanoe/Balsacanoe.html
For inspiration see http://www.newfound.com/launch_canoe.htm
and for detailed information the forums at http://wcha.org/ and http://www.blueheronkayaks.com/phpBB2/viewforum.php?f=2&sid=03f9b172d61908256d1f76c99f155520 and http://www.kayakforum.com/
BTW: main page is http://www.jemwatercraft.com . Trapper has been quite popular lately.