Hello,
Cannas a sturdy easy to grwo plants.
I think you should divide the clumps, simply by cutting through it, making smaller clumps of 3-4 growing canna plants or buds. You should also leave as much soil as possible attached to the roots. This will help the plants transition to their new homes healthier and stronger. When replanted cannas like alot of water to keep them hydrated, until their roots are strong enough.
As for the leaf rollers, i had the same problem. I used an insecticide twice about three weeks apart and it was effective. No more leaf rollers in my garden. If you do not wish to used an insecticide i have also found it beneficial to examine the leaves of the cannas as i take a morning walk in my garden. You would see the tiny baby leaf rollers on the leaves, if you remove them early you can greatly reduce the damage done, but you will have to do that a few times each week :)

Siam.