Are the variant texts within the body of your pages? Is it possible to stash them in no-indexed areas, so the only parts visible to search engines are your original content?
You would probably want to let one version of each text be indexed, because part of your audience is people searching for text. If they don't find it at all, they won't know that your site has it.
"rel='canonical'" is definitely not the way to go in this case. Where's that ROFL emoticon when we need it?