Well a freeze will certainly burn the heck out of the leaves. Now that being said,,, canna's are so robust, they've got those big rhyzomes, they should keep pumping new leaves regardless. I mean, almost any time of year, cut them back and they will return.

In your case, I'd just have a blanket ready to cover them for any forecast freezing nights.

The only thing I'm not so sure about is the benefits of doing this. From what I know, and I am no expert, I believe the canna look for soil temperature before they begin to grow. I don't know what the magic number is, but I would guess between 55-65 deg f.

So if the soil is too cold to promote growth, you may not be helping yourself to bring them out.

ANother person on this forum put a clear plastic container over his and it worked just like a mini-green house promoting growth.

Either way,, good luck!