John,
I would remove all the shredded leaves and depending on how crippled each plant may be I would likely remove all foliage within about 4 inches of the soil line. You typically will see new growth within a few days at this time of the year. The damaged areas (if not removed) opens the door for bacterial or fungal infection. I am sure your plants will quickly recover.
Good luck,
Kent

Kent, thanks for the reply. I removed the shredded leaves which were not salvageable and the foliage within 4 inches of the soil line as you suggest. They already look better - just the removal of the "dead" foliage did wonders for the way they look. Hopefully, with some decent Summer weather now, they will be as pretty as they were last Summer (my first year with cannas). Appreciate your advice. Thanks!