I've never been able to store cannas over the winter. They always dry
out and die by January. I could store them in a plastic bag to prevent
that, but then they would rot. I'm in Minnesota, so I can't just leave
them in the ground.

My aunt in Nebraska just lifts hers whole, plops them into cardboard
boxes, covers them with sawdust and ignores them until spring. Then she
cleans and divides them at planting time. She stores all of her bulbs in
sawdust, my Uncle is a woodworker and there is lots of sawdust.

Here I leave them in the ground and divide them every two or three
years.
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Monterey, California
USDA Zone 9
Sunset Zone 17