Friendliness, at least superficially. The Red Army and the Wehrmacht even held a victory parade in Brześć/Brest together.

The land claims were resolved according to the pre-war Molotov-Ribbentrop pact with some minor adjustments - the Germans went slightly further eastwards on the Polish territory than originally planned, but on the other hand the Soviets got Lithuania.

They treated Polish civillians mostly the same - the difference between Nazi concentration camps and the GULag system is not that big. Nazi Germans considered Poles subhumans only slightly better than Jews, Soviets considered most Poles "enemies of the people", evil capitalists etc.

The main difference between the Soviet and German occupation zones is that the so-called "Western Belarus" and "Western Ukraine" (Galicia-Volhynia) held "elections" to "national assemblies", which declared their will to join the Ukrainian SSR and Belarusian SSR. The Nazis didn't bother with faux elections - Western and Northern parts of Poland that had some significant presence of ethnic Germans were directly incorporated into the Reich, the Central and Southern parts with Warsaw and Kraków were turned into a German-ruled occupation zone called Generalgouvernement.

The other difference is that there were no Polish large-scale Nazi-collaborators, but there was a significant group of Polish communists who welcomed Soviet annexation, were treated OK by the Soviets and were even given some minor administration positions.