In the first fight, Saul Alvarez took the lionshare's of the purse. Splitting 70-30 on his favor. Golovkin then retains all his belt as a result. It ended up in a draw and both verbally agreed to a rematch but then time is 65-35, which is fair in my opinion. However, Saul Alvarez was caught with steroids on his system, causing the May fight cancelled. Golovkin then beat Vanes and broke Bernard Hopkins of 18 successful defense of the Middleweight crown. Now here's my take.
Canelo has more bargaining power now since (a) Saul Alvarez was suspended because of illegal substance on his system (b) He broke Hopkins record (c) he is the undisputed champion. So I think he has all the rights to at least a 50-50 split and eventhough he and his team verbally agreed on the 65-35 at the time because the result of the VADA wasn't well known yet.
But as mentioned, dela Hoya shouldered the remaining 2.5%, 57.5-42.5, but Golovkin rejected. So at the last minute, and to salvage the fight, he had to cough out that remaining 2.5% so that Golovkin will get 45%.
And as everyone who follow the first fight, it was a robbery indeed and I hope Golovkin winning. He did the damage early and I don't think that the championship was enough for Alvarez to rally to at least make it a draw.
I think you mean that Golovkin has more bargaining power now, Canelo is the nickname of Saul Alvarez. I don't think GGG's destruction of Vanes has much to do with this position for the next fight. Also, where did you read that Canelo took the major share of the first purse? Doesn't seem realistic considering GGG was the A side?