Poland alone has no chance against the Soviets, Romania is unlikely to get involved even before considering that Bulgaria and Hungary are both likely to lean towards the USSR due to unresolved grudges from WWI, the Baltic States are militarily impotent and Lithuania hates Poland more than the USSR while the British Army is little more than a token so London certainly can't arm another nation while France is far more concerned with what Germany might do while everyone's attention is diverted.
A curb stomp of Poland resulting in the 1945 boundary coming a decade sooner is plausible, nothing more.
Funny, prior to 1930 the Soviets felt that they couldn't win a war against Poland whereas the Poles felt that they couldn't deliver a knockout blow against the Soviets. Neither country had the ability to wage a prolonged war. And that's not necessarily a military statement - the Soviet government was so focused on party over people that its decisions were convoluted at best. One gets the impression that certain factions in the Soviet gov't wouldn't mind losing a large chunk of territory in exchange for placing their faction in control.
The Polish plan relied on getting their men mobilized first against a relatively undefended Soviet border. They would then push quickly into Kiev and Belorussia, liberate the locals there and encourage national uprisings to augment their own troops. They had a fair amount of support on paper in those regions. (whether it would have amounted to anything tangible was another thing). Then they would try to fight a defensive war and wait for the inevitable peace process.
Of course this was all 1927. By 1932 the situation was totally changed. The Soviets had enough troops on their borders at all times to essentially nullify the plan. Most of the resistance had been quashed and the USSR viewed Poland as a mild irritant. But there was a window up until about 1930 where the Soviet military machine was basically a shadow and the outcome of a war between the two would have been very much in question.
A bit of a wildcard from the Polish side would have been Pilsudski, who apparently scared the pants off of Moscow. Having led Poland through the 1920 war, he also had "hands-on" experience, which could be good or bad. On the other hand Polish diplomacy at the time could be described as "petty" at best and so getting aid or arms would be problematic. But you never know.. a good PR campaign plus the fact that there were a lot of ex-pat Poles in the rest of Europe might make a difference.
Most importantly, i think is that prior to Pilsudski's return to power the Poles had no concerted desire to go to war. The economy was good and the country was getting back on its feet. After Pilsudski returned then the head of state may have wanted war, but the country likely still didn't. So Poland is really going to have to be forced into a corner to go to war (as evidenced by the way the war scare in 1927 turned out) or be attacked outright. That may drive sympathy up for Poland temporarily.
Oh, and regarding Germans crossing Polish soil to fight for the Soviets (or even on the Polish side). Consider that the Poles refused to allow the soviets onto their soil in 39. Expect the same response towards the Germans in the 1920s.