Most Canna are NOT aquatic.

Folks in this forum have mentioned Karchesky Canna often as a good source of Canna and info. I've looked at their website and they have wonderful pics of their offerings. Further, they have a small category of specifically, Aquatic Cannas. This may be just the place for you to look to see some actual examples.

In Bamboo, there are aquatic varieties have adaptations in their rhizomes and roots that allow them to flourish in water. I don't know what would allow a Canna to be so adaptive. Most folks will tell you that Canna are susceptible to rot if overwatered. So the Aquatic varieties are very unique indeed and may additionally require very warm external temperatures.