Here are some good pictures and articles concerning Canna Virus:
canna virus - Google Search
Damage can also be due to excessive sunlight, too cold, wind. I personally had a week and a half of 80 degree weather in February followed by near freezing temperatures for equally as long. This will stress and distort newly emerging leaves. Here are some internet quotes:
A low nitrogen level will leave Canna foliage with yellow striata, and slow its growth rate. Phosphurus helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress. Potassium helps in the building of protein, photosynthesis that keeps the foliage a consistent green, and reduction of diseases. As can be deduced from that, deficiencies in theses basic macronutrients can result in unhealthy plants with effects that can be mistaken for Canna virus. Those are only the three primary nutrients required for healthy plant growth, and many others are required in sufficient quantities to provide healthy, vigorous growing conditions.
The virus manifests itself as a crinkled leaf. However if you are 'forcing' your plants into growth using a heat mat, very often the first couple of leaves will be crinkled and distorted. Once the plants are removed from the heat mat normal leaf formation should follow. If you find that the subsequent leaves are distorted, chances are you have a virus.
Comparing your leaf growth that follows will help in determining a plant suspect of virus.
Prevention methods:
To help ensure you don't spread the virus you will need to make sure you sterilize your tools when moving to a different plant. 10% bleach should be fine
When receiving plants from a trade or store, grow them in a container until you are sure they are healthy.
Soaking bulbs in a 5% bleach solution for 15 minutes to kill any viruses before planting.
Cannas get infected the virus will spread to all plants, because the bugs that eat off the infected plant will spread it to the next. When I have a infected plant I dig it up cut off all the bad spots on the root, cut all the black roots dip in a bleach bath, then plant in a separate container and watch it for a year. The next season you can replant in your beds. This has worked for me many times, I am not sure if you should try this (or even trust cannas bought with the virus) but if you do buy some better go ahead and bleach and plant is small pot and watch for a season, all my new plants get dipped in a copper bath before I ever plant them.
(End internet quotes)
~JaNan