We can start with the 3-40 in the playoffs last year, we can continue on to this year and see the lapses in approach and effort, we can also infer that he may not be totally clean, given the state of affairs with people like Arod, Melky, Ortiz (players he's close to, who all have PEDs in their portfolio).
I've gone back and forth on this , and I have come to the conclusion that once a new GM is in place (yes - I think Cashman's efforts to get fired will finally pay off after this season) - whether to sign Cano or not will be the decision as to the direction this team will take. Sign him? Expect more FA signings, patches, etc. Let him go? A new GM will rebuild, and there will be a few lean years. My guess? Cano signs, the Yankees continue down the road of signing FAs, and just like in 2009 - this team may stumble in to another WS 5 years from now.