/ How different would WW2 turned out if Poland accepted Hitler's offer
Anyone who has studied the War (especially in the 1930's) realize that France and England weren't prepared for war.
Yes they were, France could mobilise and equip a 2 milion strong force, Britain could muster a 100 thousand mobile army, what you mean is that neither France nor England mobilised for war in time but thats again due to their willingness to sacrifice Poland.
They not only weren't prepared they simply didn't want to fight
That much is true, neither France nor UK were willing to honor the letter of their agreement with Poland and limited themselves to token aid, both financial and military.
Poland didn't go through WWI like the French and English.
No, Poland actually went through WWI much worse than French and English, Poland was the frontline of the german-russian war and then russian-polish war, the combined military and civilian losses mount to around a milion people and the loss of 90% of its economy. That means that Poland lost about as much as France (France lost approximately 1.5 milion but was larger) and its economic losses were several times bigger and yet Poles were both ready and willing to fight.
Poland could have done better against Germany and Russia especially after the War,
After the war Poland was occupied by over a milion russian troops and could not decide about anything by itself.
after-all they were offered the Marshall Plan, but refused.
See above. They were made to refuse by Russians, there's even specific letters from Moscow which underline that "there is no need nor requirement for the capitalist aid".
Poland doesn't have a history of good governance.
So are you a biased idiot or just a troll? Poland ruled as a sole power of central and eastern Europe for over 200 years but it doesnt have a history of good governance?
a significant number of Poles after the War believed in Communism. That's a fact.
Approximately a milion, out of more than 30 milion people, that means that approximately 3% of Poles believed in communism, hardly a significant number. Poland was communist because it was sold, betrayed and forgotten by the western allies and then occupied by Russia, that's a fact.