I've recommended it a number of times on this board. It's a great cruise. Leaving from near the Musee d'Orsay, it goes up the Seine for the same sites that you would see from Bateaux Mouches (minus the Eiffel Tower). And then, as previous posters said, it turns into the Can St. Martin beginning with a long stretch under the Boulevard Richard something-or-other. Once through that, it goes through a series of locks in neighborhood Paris that you wouldn't otherwise visit.
Narration along the trip is in French and English. Our guide was hilarious. You can sit at the bow to enjoy going through the locks or you can stay inside. You can also go up top.
The cruise ends up at the Cite des Sciences - Paris' high tech museum. It's one-way trip, so you take the Metro back.
We thoroughly enjoyed it. There is so much running around in Paris that it's great to relax and hang out on a canal boat.