In about 2007 we got rid of all our cannas due to the problems with canna virus. We didn’t grow them for a further 10 years until we found, in Hart Canna , a supplier of genuinely virus free stock. Sadly there are many places only too happy to sell you infected stock and some public gardens with entirely virused plants. My advice is to get them from Hart and ignore the dried up corms in bags at the garden centre, they will only bring you grief. We have a couple of new ones for 2019.
If you have canna plants and are worried about them then check this excellent site. It will prevent you from keeping infected plants or disposing of non virused plants that are just a bit stresssed.
Cannas are, however, essential tropical garden plants giving height and colour in both leaf and flower at a time when we are usually starting to feel the fear that hedychiums might not flower in time for our openings. We grow a small seection of both green and red leafed cannas. We contrast the darker ones with a variegated arundo donax reed. Cannas seem to be pretty hardy and we notice more loss in mild and wet winters than we do in the colder ones. We dig up a few small pieces and keep them in the greenhouse over winter and split in the spring. This can yield two or three substantial plants for that year and some insurance against loss during the winter