Chelle: I don't grow a lot of Canna's but I do have a few and I've cut the stalks back and they re-grow just fine. I don't know what thread you were on but I found this while doing a search; go all the way to the bottom of this page to Forum Results (or something like that) and there are a few threads re: Canna's:
http://garden.org/search/index...
I'd look through a few but I need to finish cooking dinner.