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As long as the leaves came from healthy plants, then I do not see why not. You can add to the soil or toss them into the compost pile.

This article should answer your questions: https://extension.psu.edu/plants/master-gardener/counties/adams/news/2012/canna-lilies-care-winterization

First, there's a good probability that some of the rhizomes you planted were not viable. You might try discussing this with the store from which you bought them, possibly they will refund or give you some more plants.
However, even if they don't, you can go on from where you are. First make sure you have the best culture for them. https://www.gardeningknowhow.com/ornamental/bulbs/canna/canna-lily-care.htm
Then take up the rhizomes and store them over the winter, and plant again next year. here are some tips for over-wintering: https://www.gardeningknowhow.com/ornamental/bulbs/canna/storing-canna-bulbs.htm

To divide the rhizomes, all you need to do is brush off the dirt and break them apart with your hands, or cut them with a knife. Then, this article should help you with planting: https://www.gardeningknowhow.com/ornamental/bulbs/canna/canna-lily-care.htm

This article should answer your questions: https://extension.psu.edu/plants/master-gardener/counties/adams/news/2012/canna-lilies-care-winterization

Probably your plants have canna leafrollers, just about the only insect that troubles canna lilies. This article tells you more, and what to do about them. https://aggie-horticulture.tamu.edu/galveston/weekly_q&a/f&b_11.htm