I did this as a weekday ride once, staying south of 50 (overlapping with ewilliams’ route). From Largo Town Center, it was basically Woodmore Road to Bowie, then Governors Bridge Road to Riva. The hairiest part was getting from Riva to Annapolis; bridge doesn’t have a shoulder, the numerous inlets result in very poor street connectivity, and it dumps you into the awful sprawl of Parole.
In Maryland, I’ve often had good luck looking for “XYZ Bridge Road” paralleling a highway — seems like these were the original through-routes. Brock Bridge Road, for instance, is a nice parallel to I-95/BW through Laurel.