I dunno, but it looks to me like at least two bugs are eating your canna leaves. The yellow spots are likely due to an insect that doesn't eat plant material, but sucks juices from them. The holes and missing pieces look to be from a bug that does eat plant material.

Try using bioneem on the plants once per week to see if that solves the problem. Bioneem is an extract from the neem tree' s seeds. It has 3 modes of action. First it works like an insecticidal soap in that it kills many insects on contact by smothering them. Second it acts like Deet for plants in that it discourages bugs from landing on sprayed leaves. Lastly it is a growth cycle inhibitor for any bug that feeds on the plant. This means they cannot succesfully reproduce. The last effect is systemic meaning the plant takes on this quality internally in response to the product's application. The effect lasts a week or two in most cases.

Bioneem doesn't harm beneficial bugs (because they do not feed on the plants) and it is non toxic to pets and humans and as such is even OKed for use on food crops. It is also 100% organic in case you are concerned about such things.

If your leaves ar covered with the rust yellow spots, cut that leaf off with a single edge razor blade. If you discover spots near the base of the leaf where it meet the stem, before the entire leaf is infected, take a cotton swab and some isopropyl 91 percent alcohol and rub it over the spots. It won't make them go away, but it will prevent the spots from further advancement.