He gains a freakish amount of weight between weigh-in and first bell. Alvarez is quite short, in many ways (height, reach etc) he actually isnt that much bigger than Khan; but like Frampton he is very stocky. Id say maybe 175 in the ring. Thats about a pound per hour since the weigh in - incredible really.
I think i remember the commentator saying that he wasn't weighed on fight night for the Cotto fight. This could be because of GGG and their constant weight negotiations. The two fights previous, Canelo weighed in the 170-175 range.