You do have to dig cannas for winter; they won't survive in the frozen ground. Wait until frost nips or kills the tops, then dig them. Compost the tops and gently work the soil off of the tubers. Wrap them in newspaper or store them in closed paper grocery bags in a cool, dry place. A cool basement is ideal. The seed pods are just that--seed pods. Some people deadhead cannas so they won't waste energy producing seed, but that's optional. Cannas are generally propagated by dividing the tubers, not by seed.