Nor would the EU, of which Poland is a full member, allow them to absorb so much territory.
The EU can eat ****, they are in no position to allow or not allow anything.
---
If it wasn't for Ukraine, Russia would never have existed!
You are confusing issues here. Don't listen to propaganda and tall stories. Russia's origin is in Moscow, and medieval Kiev is only a cultural influence that ended a long time ago. Kiev and Moscow history diverged long time ago.
What you are saying sound bizarre. It is like saying that if it weren't for France, Germany would never have existed.
---
to even think about Ukraine as a client territory
That would make some sense if Ukrainians were clamoring for it. Demanding to be a part of Poland, there is nothing like that. It is a bizarre idea concocted by an American who has too much time on his hands.
On the other hand, even people like me who think that Poland lost an unjustly large chunk of territory to the Soviets and Ukraine has not right to it, don't want to extend Polish jurisdiction over the whole of Ukraine, no gain in it.
--
Just as the Russians in Crimea and Donbass.
No one cares about Russians anyway.
If they are dissatisfied, they can move back to Russia.
There is plenty of land there.
Once Russia recognized sovereignty of the Ukrainian state in 1991 in existing borders, any subsequent territorial claims are illegal and any acts that involve armed forces against Ukrainian sovereignty are acts of war.
There is no justification for the war of aggression.