How do I cut apart the plant and save the tubers?
Certified GKH Gardening Expert
This can easily be done. It is best to wait until they go dormant, but if you cut tops off and force them it will be ok also. Here is an article on dividing these: https://www.gardeningknowhow.com/ornamental/bulbs/canna/transplanting-canna-lilies.htm
Here is an article on storing them: https://www.gardeningknowhow.com/ornamental/bulbs/canna/storing-canna-bulbs.htm