There was a case of a Robin DR400 which was ditched in a Norwegian fiord. The occupants sat on the back and were rescued by a fishing boat which then towed the aircraft back to port and it was manhandled out of the water to eventually fly again. In all it stayed up for 2 hours, but it did have empty fuel tanks…
I would be very wary of assuming any type of aircraft will float. It must depend on a lot of factors like sea state, fuel, the amount of damage, etc. All the PA28’s that I know about have all sunk, if that is any indication of one to avoid, especially as it only has one door.
Rod1