Many fans and former fighters think he already is. Fernando Vargas in this interview (go to 7:35) stated that he's "the best fighter that Mexico's ever had". This content is protected
Canelo will never be held in the same esteem as the great JCC in Mexico and probably not even SS for that matter .
Best one I have ever seen, in my lifetime. Saw Chávez vs Whitaker in San Antonio Saw Canelo vs Kirkland In Houston. & Countless Mexicans on PPV. I hear the Salvador Sanchez guy was a phenom, never got a chance to behold him fight live. But I watched the YouTube vids , he was great. Canelo is the most accomplished fighter & has a lot of career left to go. will be interesting to see how he responds to his latest defeat & finishes his career.
To answer the thread title. No he isn't the GOAT Mexican although his career is still ongoing. I doubt he will make it as Mexico has a rich heritage in the sport.