When Germany invaded Poland, both France and Britain declared war on Germany as they were bound by alliance. If you say that the USSR invaded Poland in 1939, then France and Britain were bound by treaty to declare war on the USSR in 1939. Do you have any statements to this effect from Winston Churchhil or DeGaul?
Do you say that the USSR invaded Poland again in 1944 as they fought the Axis Powers back through occupied Poland? Clearly the Red Army fought on Polish soil in 1944. Was that an act of aggression against Poland?
Do you have any orders to Polish units which you should be able to point to which directed Polish units to fire upon Soviet forces in 1939?