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In your zone, you should be right on the border between where cannas can be left in the ground all year, and where they need to be lifted for the winter. I'm guessing that you leave yours in the ground. I think most people would find that spring is the best time to divide, and transplant, cannas, and I'd stick with that if I were you, since you are sort of in an iffy zone. Unless you want to dig some up now and move them just in the spirit of experimentation. But I would advise leaving most of them till spring. This article has more canna information: https://www.gardeningknowhow.com/ornamental/bulbs/canna/canna-lily-care.htm

You can trim the roots if they are quite long, but it is best to leave them intact if possible. Here is an article on storing cannas that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/canna/storing-canna-bulbs.htm

Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/canna/storing-canna-bulbs.htm

The leaves on the canna are far more susceptible to frost than the roots. Plus, the roots have the insulating protection of the soil. In your area, the roots should be fine being left in the ground for the winter and they will regrow in the spring.

I would go ahead and split the two apart and pot up the Canna in it's own pot. Then just let it grow until you are able to plant outdoors after the danger of frost has passed. I know many gardeners who start their Cannas indoors since they live in a zone with a short growing season.

Here is an article that may help you.

https://www.gardeningknowhow.com/ornamental/bulbs/canna/planting-cannas-in-pots.htm