I don't know why Michelin does not put this information on their web site. I called them, 800-346-4098, and this is a summary of what they said.
Solo: Front 32 psi and rear 36 psi
Loaded: Front 36 psi and rear 42 psi
Michelin's representative said to use these pressures. There is also a version of the Pilot Road 3 with a "B" rating.
It means the sidewall is stiffer for two-up riding. Standard is for single riding. The load rating is the same but the stiffer sidewall will help the tire stay round when two-up. They will both last the same mileage.