I'm just trying to be realistic here but of course, I'd love to see that happen again.
So as you can see the weight differential is simply too big, so either GGG moves to super middleweight or even light cruiserweight or Canelo will have to change his plans and instead of going to a heavier division move to a lighter one, something that is rare because as boxers mature they tend to move to the divisions above their weight and not to one or two divisons below their current weight.
The trilogy now is just a dream, it's far from happening, maybe after these two boxers will retire we will be able to see in an exhibition fight, but as of now, they have different plans and it's not easy to go down or go up in weight, it requires time to make it happen and I don't think Canelo's plan includes GGG now.
Stop this speculation for now until we hear positive words from Canelo as it looks like he will be the one who has to approve first before they'll settle.