"and especially the EU, which was mostly built on the basis of confrontation with Russia"
Is that a US point of view? As a european, it is the first time I heard this.
(Edit: I mean yes, it was founded under the assumption of soviet threat, but it was not constructed especially against russia, which is how I read your comment)
The NATO was constructed against communist russia.
But the reasons for the founding of the EU are more complex, but mostly they were for .. europa. Not to become dependant on russia, nor USA. Stand on its own. Interconnecting economically, to not have a big war again.
And large parts of europe would actually love to get back to also freely trading with russia. Eastern europe (starting in east germany) had tight industrial relationships with russia and were therefore also hit hard by the sanctions.
Now it seems hard, to imagine going back while Putin is in power, but 15 years ago, it all looked very different. With a radical change of leadership in russia, it would look different again.
Russia is huge and has lots of ressources, they would be welcomed back for sure.