Hey, definitely give them a try in the water. Cannas all like wet feet, and if it's warm (or in Texas, hot!) I'm betting they'll go crazy. You may have trouble keeping them in check.
But I wouldn't put them in the water until the water is warm.
I've tried various Cannas in my pond here, and they've all done fine. This year, I have extras of the Tropicannas with the crazy stripey foliage - they multiplied nicely last year in pots under the downspouts. Going to give them a try in the pond.
