If your Canna leaves are not unfurling, this is probably because your plant has leaf rollers. Leaf rollers are a common pest for Cannas. To check for them, look for small silken threads that sew the leaves closed and keep them from opening. If you see these, you have leaf rollers on your Canna. Unfortunately the only way to get rid of leaf rollers is to completely cut the plant down to the ground so that it can grow back again minus the leaf rollers

Do not compost the plants that you cut. Leaf roller eggs can survive the composting process and you'll end up getting them on your Cannas again.