If you're going with wood found on earth: Generally seen, the lighter the wood, the less durable it is. For dugout canoes, the ideal is a wood with dense and long fibers. Sure, that is heavier, but its more likely to survive outside flat water. If on the other hand you're building a canoe with framework and a thin shell on the outside (bark, hide, etc), then you would end up with something lighter. 

An eight-man canoe isn't much for scouting, generally speaking, but it is better than a hundred-man canoe, of course. When you scout, you want to be quick and maneuverable. For a pure scout canoe, we'd suggest 1-2 man. Its only when you need to move a lot of cargo or men that you need larger. Seeing as you're intent on moving numerous folks out of the city, we'd go with a canoe designed to transport a small group. A hundred-man dugout isn't very maneuverable or quick to build up speed, but a 1-2 man canoe doesn't have room for more. A canoe suited to hold 8-10 seems decent for that purpose. Its not the quickest out there, but if everyone helps, it can be quite fast. Its also not so large as to be very hard to maneuver. One advantage with canoes over regular masted boats is that they're much harder to spot. Which comes in handy when fleeing. 

We'll get a post up later on.