Maybe you've watered them too much?

Here in zone 8a, cannas stay in the ground year-round, & this exceptionallly mild & wet summer I didn't water mine at all.

The first "killing frost" (a hard freeze which damages plants)kills the foliage, & I cut it off & put a little mulch over the rhizomes.

That's all.

Period.

Here, cannas are so carefree that they're a landscaping favorite of gas stations:

I'll bet they're the same where you live!

Cannas growth will slow down as the temperatures drop. The browning of the leaves could be overwatering or the drop in temp. Slow down on the watering let it dry out somewhat. HTH, Tara

That is probably it- we just finished rainy season. I will cut all the dead stuff down and see what happens. If they predict rain, I will move them under the porch for a while. Thanks- Gwenn