I've never had to deal with leaf rollers, so I don't know if there would be a less drastic way to attack your infestation or not. If not, go ahead. Healthy rhizomes should certainly have enough energy to send up new shoots, and they'll have the whole summer to recover and bloom.

If you go to treat the bed.I used bayers advanced tree& shrub insect control spray.In march I removed old mulch and some of the soil& even moved some from one bed.The ones i trearted have no damage,but my bengal tigers have some damage but no neew since sprayed(3rd time yesterday...every 7 days) I read they can overwinter in the soil.was a gardening article in some washington paper about their overwintering eggs and their eggs are in soil and emerge with foliage.

I live in East Texas and the leaf rollers are bad this year. Here the little moth/butterfly which is only about an inch in wingspan flies around and lays the eggs on the plants. These butterflys seem to ba around as soon as the foliage starts to appear so the same thing may be happening where you are. I spray with the ortho systemic and that works well although I have to keep applying it as new leaves appear. I heard that the bayer tree and shrub or the rose care works but you have to have it on the soil before any growth appears. I will try that next year. Good luck the cannas are worth the effort.

You may want to try BT (Bacillus thuringiensis) - I tried a water based spray of it on my Cannas (1st time having leaf rollers for me) and it took care of those leaf rollers. It is a biological insecticide that destroys leaf-chewing worms. They ingest it while munching on the cannas and it basically destroys their digestive tract, obviously leading to death. You have to reapply after rain & probably as new ones hatch out.
Good luck!