Commandeering a spell with rebound?
The real outcome is that Rebound doesn't do anything: it doesn't get exiled, and nobody gets to cast it again.

The definition of Rebound in rule 702.87a says


  Rebound appears on some instants and sorceries. It represents a static ability that functions while the spell is on the stack and may create a delayed triggered ability. “Rebound” means “If this spell was cast from your hand, instead of putting it into your graveyard as it resolves, exile it and, at the beginning of your next upkeep, you may cast this card from exile without paying its mana cost.”


In your scenario, your opponent cast the spell, but you control it as it resolves. This means that you didn't cast it from your hand, so the condition isn't met and Rebound doesn't do anything.