I have to say I'm kind of surprised it was testosterone even though it does seem he lost quite a bit of weight. I always liked his game but always thought he was too out of shape for the type of game he has.
Quick story - Cano and Melky are close to my age and used to go to the same venues as my friends when they were with the Yankees. Lets just say the Yankee brass purposely got rid of Melky because he was hindering Cano's development by pulling the Micky Mantle routine. At the end of Melky's career at the Yanks he left those bars (due to being tossed out of many) and started to go to even shadier establishments in Spanish Harlem (not all are bad places but some are known for their extracirrcular activities and ties with gangs) and thats when the Yanks cut him loose. There is no coincidence that when Melky left that Cano's numbers improved and the Yankees set him up with a better support system.
When I used to hang out with Red Barron then Yankee Triple A players in Scranton they always said the same thing - If you're not cheating you're not trying. Since then two of them have been suspended for PEDs.