He won't be fighting Joseph Parker. Parker will be fighting on the Usyk vs Dubois II undercard on July 19, although there were talks of him having a headline fight in New Zealand against Justis Huni prior. Whyte won't be fighting anyone good on June 7. It's a run-out basically.
Not expecting much opponent wise in such short term notice. Okolie, Gassiev, Hughie Fury or someone like that would be reasonable options for Whyte. Will probably end up being against Demsey McKean.
It won't be Parker. Hrgovic would be ideal. He would likely take the fight on short notice. But someone like Adeleye, Dacres, or Webb or a European journeyman is more likely.
I also assume that there will be nothing from the fight with Parker because Parker would flatten him in the early rounds, it could be a Hughie Fury caliber fighter.