Q.Cannas
Should canna foliage be cut back during the winter? I live in California’s Great Central Valley, so our winters are fairly mild. Thank you, in advance, for your advice.

Even in warm zones your Canna's will need some winter care.
Trim the foliage back on the Canna's even if your not going to lift them and divide them.
Add some hardwood mulch to help with temperature fluctuations and keep them from drying out. Only water if the ground becomes to dry.
Do not fertilize in the winter.
https://www.gardeningknowhow.com/ornamental/bulbs/canna/storing-canna-bulbs.htm