We can make another comparison to JMM/Pac. Marquez was almost 40 and was facing Pac who was coming off a loss to Bradley, and everyone was claiming they didn't care for the 4th match but it still did over 1 mill PPVs. Both Canelo/GGG fights did over 1 mill and my guess is this one will do slightly under although the bad economy might put a bigger dent than expected.
I wouldn't say way bigger. GGG was untouchable for over a decade and Canelo is probably the biggest superstar in boxing today