With a most strip built canoes, there is not a great amount of rise in the shear immediately before the termination at the stem. It's likely that you won't need to steam them if that's the case.
Call around for some long hardwood lumber. If you can't find 17' stock, you may need to scarf joint a couple of shorter lengths. Or check the builder/restorer page on this site, and either buy stock or have them mill up a pair.