Is Anna gonna be back this season? I haven't heard anything on that. But either way, I don't see them getting married and shacking up. I'm a fan of Jo, but Jensen and Alona just don't seem to have much sexual chemistry, so I'm weary of them going down that road again (but if the chemistry WAS there, I'd be all for it). I'm sure Dean will have his usual flings at any rate. :)
As for Sam... he'll probably have a few flirtations on his days off. :) I'd love to see him again with Sarah Blake! They were adorkable together. :D