Right now any kind of CM will do. Personally I would go for a more versatile type of CM than Canales like Holtby who can play a straight CM or AM. I remember us being linked to Adrien Silva from Sporting a while back and he seems like the exact kind of player we need right now. Also echoing a post above, Canales is horribly injury prone isn't he? Would be a bit funny going for him at this time.
The other option would be getting a winger and having Pienaar/Barkley/Mirallas for AM and Barkley as backup to Barry/McCarthy. Although I can't imagine shifting players all over the place is the best for getting a consistent starting 11.