How can I protect my canna lily plants from whatever is eating them?

Japanese beetles eat on my cannas. Now the beetles are gone the cannas are doing well.

looks like worms, Lowes has an organic oil I use, neem oil. Mix it in spray bottle and spray it good , make sure to get under and down at the base of plant

Canna leaf rollers (worms). Yes, use neem oil spray like Dorothy suggests.

Try Neem oil it’s an insecticide that I use on my vegetable plants that is used by organic gardeners.

Looks like Japanese beetles to me. I deal with them too... Japanese beetles are black and have a golden / copper-ish shine to them.

Best way to get rid of them is to have a bowl of water with some dish soap readily available next to the Cannas.

When they appear - 'pluck' them off the leaves, (carefully look under the leaves too - as they startle easy and will fly away) and make sure to get them into the soapy water.

I find wearing a pair of garden gloves works best. Japanese beetles to not bite or sting, however, they do have a prickly feeling to them.

Disposal is key. The smell of dead Japanese beetles WILL attract other Japanese beetles to your Cannas.

Best disposal is to flush them down the toilet once you have a bowl full of the lil monsters.

The more you get rid of the more they lessen until they are gone - until next year sadly.

Hope this helps!