Poland did control a vast swathe of territory in western Russia in the 18th Century, before they began being mutilated by their neighbours in the Partitions; possibly, at a pinch, the Polish government might have been willing to help Germany in order to get those territories back. However, Poland may have invaded Russia in 1939 with the blessing of Germany and the promise of German backing, only to then have the GHC effectively turn their backs on the Polish war effort by taking on western Europe in 1940, in order to reach the Atlantic coast and control the whole of Europe. In that case, Poland is left to take on the Soviet Union on its own, with the Polish armed forces as they were in 1939; not a good prospect for victory.
Alternately, if as on OTL the Germans managed to take over western Europe relatively quickly, they could have left those territories in the hands of occupation forces and turned their attention to helping the Poles in the East.
Alternately again, if the Germans and Poles had agreed to launch a mutual invasion of the USSR in 1939, the Germans might have been quite happy to leave western Europe to its own devices, merely placing a defensive force along their border with France, Belgium, Luxembourg and the Netherlands. With Switzerland and Scandinavia neutral, and with Italy, Spain, Portugal, Austria and Czechoslovakia essentially in the German camp, the Germans and Poles could have concentrated their attentions on the USSR, and had an a war based entirely in eastern Europe.