My experience with Canna is that you can divide them almost any time. They are very hardy; so much so, that they could be called invasive and weed-like.

However, I would not divide them when they are under stress. Your chances of loosing them if any, will exist then. For example, I divided some under very Hot dry conditions in mid-Summer and the newly planted ones wilted and did not look good for about 3 weeks. Of course, that did not make me feel too good. But then they magically perked up and are now doing fine.

If you have just experienced a frost and they are recoiling from the frost, wait a while. There's no hurry. Although they may survive if you do it now, it's just good practice to get into, to not get ambitious when your plants are under stress. And it'll be less stress on you. :)

If you are like me though, and like to experiment in order to learn, divide away one and replant it and see what it does next Spring. But wait on the rest till a less stressful time.

Thanks for the info. I'll just wait til we've had a couple of good rains and we can dig in the clay "soil".
NT