To me it would come down to how much that canna meant to me. For me being in the same zone they are my most forgiving tropical and I admit to abusing them on a regular basis,
I see no reason at all that your plan would not work. Just make sure it is a well draining spot for cold wet temps . A good mulching around the pot would be an extra safe guard. But really in zone 8 I think you will be cool. I .have seen down to 17 F and cannas were fine in ground but never came back from frozen water. Miles may very.
I say divide and share your experience
