I think it's probably pretty good, he's been in the ring with some guys who can crack and whilst some of them were a bit shopworn he's taken enough to show that he can handle a decent shot.
Canelo has been in the ring with power punchers on many occasions, and his chin has been tested. Yes, his chin will continue to get tested, but as of now, he's shown great whiskers. Miguel Cotto 73% KO ratio KTFO Sergio Martinez and Daniel Geale most recently James Kirkland 82% ratio KTFO Ironed Chin Alfredo Angulo Shane Mosley 68% KO ratio KTFO Titanium Chin KTFO Ricardo Mayorga
His chin surely pass the test at 147 and 154. Now that he invade 160, we would have to wait and see, there are massive punchers in GGG, Jacobs and the Charlos.