Cannas are naturally from tropical and sub tropical areas along the margins of forests and often grow in marshes and even in water. Therefore they do not always do well in full harsh sunlight, in exposed locations, and with their roots too dry.
Try growing them in a large pot with some amount of shade and keep them sheltered from the wind. With nice damp compost they should recover and go on to flower. It is possible to grow them from seed early in the season and still get flowers the same year.
Keep persevering as they are beautiful plants. You might like to grow some of the species ones from seed.