Yeah, defense is so hard to quantify with the naked eye. I can see why you think Cano looks like a good defensive player because he can make some spectacular plays and he has a great arm. To me, the thing that really limits him is his ability to make the routine play, however.
UZR really isn't a fair indication of a player's ability in such a small sample size. It's the only legitimate, objective measure of a player's defensive ability that I know of though. I'm sure we'll be revisiting the UZR stats throughout the year.