Was there any example in canon or legends showing a landspeeder moving over any body of water or swamp? Or any other vehicle that implemented repulsors like the AAT.
Though some of the answers depend on if you would allow airspeeders, they use repulsor lift they just fly higher.
GAR Infantry Support Platform AKA Swamp Speeder
The Swamp Speeder as the name suggests is a repulsorlift vehicle that hovers over swamps, modeled after a fan boat by designer TJ Frame.
It can be seen in Revenge of the Sith operating on Felucia, a tropical jungle world.
Heavy Missile Platform Droid Gunship
These Confederacy repulsorlift airspeeder were present at the Battle of Kashyyyk and were shown flying over water in Revenge of the Sith
This New Republic airspeeder was shown to fly over water in the Battle of Mon Calamari in the Legend comic Dark Empire
And from issue #12 of the Marvel Star-wars comic these Hydra-craft
Thanks to Valorum
In addition to other examples, in Episode I we see two land speeders floating in Theed once Obi-Wan and Qui-Gon surface (3 minutes 30 seconds).
They look exactly like some of the models we see later in the movie on Tatooine. They seem to not only be able to hover on the water, but in some cases, float when parked.
On the same planet, there are Gondola Speeders, only seen once in the movie. http://starwars.wikia.com/wiki/Gondola_speeder