I don't think Floyd takes fights he sees himself losing. There are only few boxer out there who are as smart as him. Calling Canelo a cherry pick is obviously nonsense as it's the fight we all want to see, but I'm absolutely positive Mayweather chose to participate in a super high profile fight again because he knows this kid stands no chance.
I don't think most fighters take fights they expect to lose. At least not top level guys like Matweather. He can be beat, but you are right not likely on Sept 14th.