Split topic from "Solution for Chechnya" thread as last points were off-topic, but I do think this is relevent discussion for own thread.
IMO Slavic Union/Federation would inevitably have more Russian influence (not necessarily hegemony) over union, because of following:
1) Russia's economy is largest of Slavs. Even Poland's economy (second biggest of all Slav ones) is 1/3 of Russia's.
2) Russia practically feeds oil and gas and other natural resources to Slavic lands (of course Russia needs money in return).
3) Russia's military capacity (especially strategic) far exeeds any other Slavic army.
But rest of Slavs put together would never permit any sort of Russian hegemony and I doubt myself they would want it as opposed to just being equal partners. Sure, it would be like Germany or France in EU, but I think they learned from Cold War that other Slavs do not like living in someone's else's hegemony and would try behave more like equal partner than big tyrant.