[RightWhale]

Would it be entirely possible to have seen a major battle and possible bloodbath in Philadelphia or Baltimore?

They were headed to Baltimore, a new port, and would have created general havoc there. A major battle? Not necessarily, if they burned everything and left.

[Non-Sequitur]

They were headed to Baltimore, a new port, and would have created general havoc there.

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.