I predict GGG by majority decision. Always some questionable scorecards in Canelo's favor. Canelo has conditioning problems and is a bit smaller than he was during last year's weigh-in, he does have the better boxing skill but that won't be enough to beat GGG.
I think you\ll see pretty much the same fight as the first one, and probably a similar decision, perhaps this time going all the way and giving it Alvarez if he can manage to have even a few more good moments.
You're not likely to suddenly see any different version of these two fighters. Golovkin is 37 and set in his ways, he's speed and reflexes aren't going to be more than they were 12 months ago, the best he can do is duplicate the same effort.
Canelo has been pretty much the same fighter for 50 pro fights, he's never been particularly energetic and it's probably time to give up any notion that some busier or more aggressive version of Canelo will finally show up, if it was in him we'd have seen it by now
Fortunately for Alvarez, he has a politically built in 2 or 3 point lead before the bell even rings, knowing that Canelo can stay within his comfort zone, require Golovkin do the work and take all the risks, knowing he won't lose on the scorecards as long as it's not totally lopsided.
The only real wild card will be if Golovkin this time around accepts the fact he simply can't get the decision in any ind of competitive fight and decides to go for broke and take all the risks in search of KO or at least so,w 10-8 rounds. If that happens, something could definitely give - but I wouldn't be 100 percent sure that the 8-years older fighter will automatically benefit from forcing a more torrid pace.
Boxing isn't as popular as it once was, but this is the biggest fight of the year and it will attract casuals and lots of celebs ringside
Even more reason to doubt the scoring would be different this time around. Alvarez has another 6 or 7 years of box office potential (for reasons which totally escape me...) Golovkin is a declining fighter with at best one or two big events in him and even that would be only one quarter the revenue of Canelo's fights, so business wise it's a no brainer ...