If Pilsudski had managed to created a greater Poland with Dnieper as eastern border how would this effected ww2 or inter war relations with USSR.
I don't think it would change relations with the SU, Germany, Lithuania or Czechoslovakia much. Poland bigger may make for closer relations with France and Romania though (since Poland is bigger, both may worry less about the country being snuffed out). IF those happen, that should have positive effects on the economy (due to a little more investment money being available).
Much depends on how the Pilsudski arranges this larger Poland politically - personally, I doubt that either the Poles or the Ukrainians would accept a unitary state. As such, we may see a federal Poland (the NDs wouldn't like it, but I bet they'd like it better than Ukrainians deciding who the next Polish government were). Or it may be seen as more important to have a strongly unitary government (as OTL), which means that autonomy would be pushed down to the provincial level...
If Poland is as unstable early on as OTL, or more unstable, then being bigger doesn't help a whole lot, and this "Great Poland" still ends up crushed between Germany and the Soviets somehow.
So much depends on exactly how and why Poland has expanded further. However, since Poland being larger is almost certainly a result of Pilsudski being stronger, I'd say the odds are that Poland gets a more stable political system than OTL, which helps ALOT.
While the new lands in the East won't really be very rich, it'll still make for a more integrated economic unit as well. Combined with a more stable 1920s, it's quite possible that Poland would be a minor great power like Italy come 1939.
Poland being on the same level as the Italians in 1939 is bad news for a Germany that wants to pick a fight. We may see a situation where there is no WW2 as we know it, where a German-Polish war is delayed until the mid-40s or where WW2 starts with a German attack on France.
If Poland is weaker, but still stronger than OTL (and has more space to retreat into when invaded), it would likely be crushed after the Germans and Soviets make nice (if they make nice), but it is likely to hurt the Germans badly enough that if Britain and France are allies as OTL, France and Britain will be able to stomp Germany flat at their leisure. (The invasion of Poland took alot out of Germany and even small things to help Poland make the fall of France impossible for the Germans to achieve.) Of course, in this scenario, the East still becomes Soviet, but millions upon millions of Poles survive the war.
fasquardon