Can you give us more of an idea what the possible problems are? You're original post kind of hints that it might be sinking on you when you put it in the water, but that's not totally clear.
How does the canvas look? Is it in good shape, or does it have obvious cracks?
Any broken ribs or planks?
Any obvious rot in the wood? The stems are a common place for rot to start.
One great online resource is the Wooden Canoe Heritage Association -
http://www.wcha.org/___________________________
No your other left!
www.loonislandoutdoors.com