He may be the current lineal champ at 160, but let's face it, he is not the real champ at 160...that belongs to GGG. GGG is bad news for Canelo...either he faces his destiny against GGG or simply vacate and fight another day. Sun Tzu would approve.
He hasn't fought as a Junior Middleweight in over 2 years since losing soundly to Mayweather. He is the Middleweight champion. I don't think he should drop the big title he just picked up. That doesn't make much sense. I would expect HBO makes a huge offer to Golden Boy to make Canelo/Golovkin involving guarantees for X amount of Golden Boy fighters headlining in the next year, etc. It will be a tough negotiation for both sides.
Cancelo is as much a legit champ at 160 as RJJ was ever a legit champ at HW. He'll drop his belt and disappear just like RJJ did when they realize they came to a division that's too big for them.