For a discussion of determining value, see the post at:
http://forums.wcha.org/showthread.php?57-How-much-is-my-old-wooden-canoe-worth
In addition to the factors discussed in that post, consider the location of the canoe relative to potential buyers. While people living in central Maine have a higher than average interest in boats and canoes, there just are not very many people living there. Further, transportation/shipping of the canoe can be a serious issue that will likely affect price.
A few years ago I bought a canoe on eBay located in Mattawamkeag, Me. We live in Brooklyn, NY, and probably would not have considered the canoe at any price, except for the fact that we also have a place in in Dover-Foxcroft, Me., about an hour from the canoe seller. As it was, we were the only bidder. If that canoe had been located in eastern NY, Conn., MA, or even southern ME, I would have expected more bidding, and it well may have sold for quite a bit more than we paid for it.
Also, while a trailer can be a desirable asset, not everyone wants or needs one, and because it raises the price, may drive away a potential buyer. On the other hand, there are likely people who want a trailer, but are not interested in your particular canoe. You might consider selling and pricing them separately, while offering a "package" price for both.
As a WCHA member, you can place a classified ad here on the forums or in Wooden Canoe, our journal. An ad should include basic information such as condition and length (it’s surprising how many Craig's List and other ads leave this out), and some good pictures always help -- look at several existing ads to see what works and what doesn’t.