Let's see. One lost to the dominant small man of his era, the other dominated him in fashion no one had ever dreamed before. One's ceiling was Light Heavyweight, the other beat the Heavyweight champ and several CW sized contenders. One is avoiding his biggest challenge in his twilight years, the other beat an ATG Light Heavyweight champion at 42. Dunno, but I think I might go with Canelo.
I honestly don't know. Its impossible to tell how skilled Fitz or his opponents were because the video we have is of dreadful quality. My guess: Canelo has beaten boxers who are much more technically skilled and fundementally sound than the guys Fitz beat. But Fitz fought men considerably larger than him and even beat someone big enough to be a modern day cruiser in Corbett. I think Fitz is a greater fighter in his era than Canelo is in the current era even though the guys Canelo beat are technically and fundamentally more skilled.
82-years. That's how long passed from the first LHW world champion until the first time the LHW world champion became the HW world Champion. It's not happened again in the 40-years since, either. It's therefore utterly absurd that 88-years before Michael Spinks beat Larry Holmes, the lineal MW champion because lineal HW champion. A feat not repeated in the ensuing 127-years & surely never will be, though admittedly HWs are obviously much bigger now. Add that to the fact that Fitz didn't just beat, but utterly dominated the then p4p GOAT time NP Jack Dempsey and incredibly won the LHW world title way past prime aged 40, in an era when 40 was considered as old as 50 is today, and you have my #6 p4p boxer of all time. Canelo has a deep win resume, but his achievements don't come close to those of Fitz.
Resume Fitz(for his time) P4P Canelo. I know you look at them and see a MW who climbed to HW and one who could barely get to LHW but Fitz was really a HW who liked being superlight. He was not a MW climbing to overcome his size disadvantages he had the power advantage in every fight he was ever in that didn't really matter hence why he was comftorable giving up so much weight. He was a HW who could cut down to MW and keep his HW power and used it to terrorize MW. There are loop holes to the weight based meritocracy. This is one of them.