Imagine for a moment a world where the Soviets do much worse in WWII and the Western Allies do much better, resulting in a Cold War with the Iron Curtain moved substantially further east. Most of prewar Germany (with obvious exceptions including East Prussia) are occupied by the Americans and British, and Poland ends being liberated by the Soviets in the east and the Americans and British in the west. While the victors initially plan on integrating their Polish occupation zones into one state, the postwar breakdown in relations between the two factions leads to this not being realized, with a West Poland and East Poland coming into being.
Perhaps this scenario is far-fetched. I'll concede that. But in a world where the whole of Poland's borders look roughly similar to OTL post-1945 (i.e. the Soviets annexing Kresy but Poland being compensated with German territory in Silesia and Pomerania regions), what would be a remotely logical way to divide the country such that the two halves could be viable states?