The new card 'Warp Lightning Cannon' says "Attach to a target unit. Corrupt that unit" as t's targeting condition. Can I play this card on an opponent's unit to corrupt it?

Yes, but he would restore the unit it at the beginning of his turn and blast the frak out of you with it.

Nonetheless it could be useful to make way for your final attack!

Hmm, i like that idea.

Or at least he would restore the unit and blast you with it if you corrupted a unit in his battlefield. It would have a much smaller effect if you target a unit in their quest zone or kingdom. Especially if then light the zone on fire before they have a chance to restore the unit obliviating any need to continue attacking that zone.

Also helpful if you have the Nurgle Sorcerer and several Chosen of Tzeentch sitting in your quest zone (assuming you have the resources to fund the actions).