Are those Cannas in the bog that are struggling?
I have found they need to be acclimated slowly to a fully aquatic environment. I can only find ones that are planted fully in soil. That soil is usually a soil-less mix that is really loose. I keep them in their original pots and water daily, sometimes a few times a day, for a week. I then poke a few more holes in the pots and place them on a shelf in a couple of inches of water in the pond. After a few weeks of that, and new visiable growth, set them in a little deeper water for a week or so. If they continue to grow, or at least show no set backs, I remove them from the pots and plant them directly in the substrate in a shallow (2-4" deep) shelf. I have also found the purple/red leaved varieties work best for me.