Here is the idea, Sherman finishes his campaign a few months early being very successful, instead of going to the east, Lee pushes forward further west.
Lee runs into Meade somewhere in SW Pennsylvania, but also gets slammed into Sherman's returning forces from the west causing a huge confederate slaughter.
The most logical place would be Canonsburg just outside of Pittsburgh.
Is this scenario plausible?
Wouldn't it be more likely that there is a series of small engagements between the ANV and AoP first, leaving time for Sherman or portions of that army to get between Lee and a route back to Virginia? Then the decisive battle takes place with Lee forced to attempt a breakout through the AoP, or face being surrounded by multiple Union lines.
If that battle is at Canonsburg, a quick glance at the map suggests you'd need someone around Morgantown. That leaves Lee the only option of forcing battle or moving further and further from any reinforcement as skirmishes whittle his army down to nothing.
But before that can happen, why would Lee take the ANV into western Pennsylvania? In the east, the offensive campaign could have theoretically endangered DC, Harrisburg, Baltimore and so on. In the west, there's Pittsburgh... But wouldn't that be a damned dangerous thing to do with the ANV? While Lee is moving through the Alleghenies in PA or West Virginia, what's to stop the AoP from rushing on to Richmond?
It's a neat idea, but it needs some reasoning to make it work.