Why not do a temporary light protection (fleece, burlap, leaves, mulch) until you are able to lift the plants for the winter? I do understand the dilemmas and tricky choices - gardening is full of them - but if we can shorten the odds with a bit of intervention, it gives you time and peace of mind.

Also, even though there may be ground frosts to contend with, the soil is still usually warmer and the roots should have a bit of protection until later in the winter when chilling is deeper and more consistent (altho' I garden in a temperate zone and have no experience of US weather, so any advice or suggestion from my end should be taken with a degree of scepticism).

light frost will only affect the top growth and won't harm the rhizomes at all. The ground has been warm all summer - it insulates the roots of plants and it won't be until later in the season that the freezing temperatures will penetrate to the depth of your canna roots. The soil in the ground warms up slowly and cools down slowly compared to the air temperature.

Your cannas will be fine if you dig them after Oct 13, I would never put rhizomes, bulbs or any other underground plant structure out in the sun for any amount of time - they really aren't designed to take ultraviolet (sun) light and would probably get sun burned. After you dig your canna roots, shake off the soil and put them in your garage if there are freezing temperatures outdoors, put them on some kind of rack or find a way to provide good ventilation all around the rhizomes while they dry and cure for the dormant winter period. Or if your outdoor temps are above freezing, put them under a tree in the shade for a week or two. Store them at room temperature over the winter but not close to a furnace or other heat source, it can dry them out excessively which isn't good for them. Good luck with storing your cannas over the winter!