Hi chica, when I lift my cannas I remove all the soil off them and split the roots so that I have 2 or 3 shoots on each section, that way they will be a more manageable size for repotting in feb into pots to get them started early in the greenhouse. Don't forget to cut off all the leaves down to about 3 inches, make sure they are dry and then store them in a cool frost free place.
Ive never allowed the leaves to die back down into the root but havent found any lack of vigour or flowers because of it