Super Joe slaps his way to a 12 round points decision. He could take a shot, he could adjust his tactics mid fight he could box inside and out. Canelo has power yeah and more of it. The thing is Joe could get up off the canvas which he would in this one but just cause Canelo too may problems as he'd be jabbing away when he's not all up in Canelo's face rolling with the punches and landing hooks and straight lefts. Canelo is a very overrated boxer and Joe get's this one. Unanimous points decision he shades it by two rounds.
Since super middleweight is the weight class where Alvarez has notably slipped this can actually be two answers. I think the Canelo of 2020 and 2021 beats Calzaghe by scores of 115-113 or 116-112. The post Golovkin / Bivol version of Canelo loses to Calzaghe by the same scores.
Joe himself had power: he twice decked the iron chinned eubank, don't forget it, so we might see miss canelita in trouble
Calzaghe's foot work is too good, Canelo doesn't have the power to stop him and Calzaghe's work rate would overwhelm Canelo round adter round. It wouldn't even be competitive.