To get Poland to work with Hitler you need to make the other options worse. A rebuffed attempt of alliance with France (say, the French sentiment of "not dying for Danzig" is more widespread due to a stronger propaganda activity within France) or someone more crazy - or less predictable at least - than Stalin in Moscow. Trotsky with his "revolution export" ideology would work in this case - however it is doubtful that Hitler would still get to power in Germany. Even if he does, he will do so under very different circumstances (I assume that Trotsky would rather push KPD to co-opt SPD, or at least induce a split in SPD and co-opt the left wing, instead of dogmatically alienate all social democrats as KPD did under Stalin's orders).
A unified "Volksfront" resulting from this would probably still not win elections but result in a military clampdown and a Schleicher dictatorship with some pseudodemocratic fig leaves - e.g. a figurehead elected Chancellor. Hitler will remain a fringe figure or just one of the many right-wing radicals trying to influence the military junta. This may actually give you something Poland may agree to work with (albeit with one hand deftly clamped around it's figurative nose) - you have a more scary Soviet Union on one hand and a somewhat more predictable, although still nasty, Germany on the other hand.