I hope I am wrong, but this fight is somewhat like Ward vs Kovalev to me, in that, I will be picking against who I actually thought won the first fight. So to me, Canelo is the favorite. Slightly. 55/45 for Canelo, just imo. Wheras the first fight I had it similarly close but leaning towards G. I can see why someone would be favoring Golovkin though... its not usual to go against the guy you felt won fairly comprehensively in the first fight.
GGG won the fight in the minds of everyone who's not a Canelo fan or on a Goldenboy payroll. GGG goes into this as a favourite for that reason. The bookies ain't dumb, we all know what happened. GGG is up against it though simply because he's against more than just 1 man in that ring.
As far as sport is concerned, GGG should be the heavy favorite. Canelo's past with judges even the odds though. Not a fair bet to take, IMO. Judges could be either corrupted again or tempted to make things right the second time around alla Lewis-Holyfield 2.