I agree with dreamer2's route. Rent the car at Copley, then take Storrow Drive, then the Tobin Bridge. Traffic would be really bad on some parts of this during the week, but won't be a problem on Sunday.

After you leave Boston, there won't be anything scenic on this route. In fact, a lot of it will be pretty ugly. But I'd do it anyway. If you want to inject some scenery, I'd suggest heading all the way to Salem, and then making the short jaunt back down to Marblehead, which is a quaint and well-preserved (and expensive!) old town on the ocean, just south of Salem.

After Salem, are you going to Gloucester? Great place to visit with a car. We enjoyed a relaxing hike at Halibut Point S.P. and Pigeon Cove for a meal.
Bleason