Would that be wrong? It would be a Middleweight bout against champions. Or does it only matter if he fought Golovkin? You know that's what you want to say but what does he gain?
Same line of thought as I have of RJJ winning the HW strap against Ruiz. Impressive for sure, but not out of this world amazing
Ruiz is only 6'2, has limited boxing skills and only lasted as long as he did due to his hugging and half descent punch. He was basically ripe for the taking for a faster, more agile fighter.
You could rest assured that Canelo would not negotiate lower than 158. But BJS would probably go as low as legitimate MW, ie 154.1, just for the payday and the opportunity to beat a legend. In the Canelo case, he'll drain down good(GGG) or big MWs(Quillin, Jacobs, Eubank Jr, but for someone like Rosado or even Lara should he move N, Canelo would come in at limit.
Mayweather and Saunders can't share a ring. It would create a universe-destroying paradox to have two such massive forces of slickness occupying the same space.