I would suggest you dig and protect them for winter. While Canna sp. are hydrophytes, they are not 'aquatics' and the rhizomes subject to rot when kept in cold, flooded conditions. Canna flaccida is native to my area and while it does grow well in seasonally flooded ( but not submerged ) conditions, winter is the dry season and when it is cold/cool the ground never freezes and the rhizomes are in conditions too dry to promote rot.
Truth is not what you want it to be; it is what it is. And you must bend to its power or live a lie.”― Miyamoto Musashi
"Knowledge speaks, but wisdom listens." ~ Jimi Hendrix
“The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge.”― Stephen Hawking
Craig