Não, não é mesma coisa.
Carpool hints you know the person that is going to give you a ride, it may have a return favor (another ride, I mean) by you (if you have a car). If that is not the case, you can be going to work (for example) with someone (a co-worker, for example).
Now in Portuguese:
carpool - carona solidária/dividir carona.http://www.wordreference.com/enpt/carpool
Some time ago, there were a lane in the Rio-Niteroi bridge that was designated (on workdays - not weekends) to carpoolers.
The intended effect was to promote people to car sharing (take a friend or group of friends to their office/workplace).
This way, discouraging the lone driver to get one more car to the streets, relieving the city of big traffic jams (or at least lessening it a little bit).
Would be a win-win situation, since traveling by that lane would get them to the other side of the pound faster, and the city would have less cars on the streets.
In your case one couldn´t get a carpool, perhaps a "canoe-pool" ha ha ha. But then, canoes would have to be as popular as motor vehicles are (to have the reciprocal ride in play).