What an excellent gift! Here's a couple of ideas you might pursue:
Big City Mountaineers: I don't know if they take gear donations, but they might be able to direct you to another organization related to their mission that might be able to use the canoe.
Girl Scouts of Colorado Outdoor Adventure Club: Again, not sure if they would accept the canoe itself, but the contact listed at this page might be able to put you in touch with some of the folks who run and operate Colorado's Girl Scout Camps, who could have use for it.
These were my first two ideas, but hopefully you'll be able to develop some leads! Thanks for your generosity!