Then they were taking the scenic route. Gettysburg and central Pennsylvania are nowhere near Baltimore, and Lee wasn't even heading in the general direction.
With that said, would it be more of a possibility that Philadelphia would have been the city in question instead of Baltimore? As you posted earlier Non-Sequitur (at least I think it was you), this would have been assuming that a lot of things happen before and even during Gettysburg and your comment that the South was simply delaying the inevitable anyway.