Cruz would be the plaintiff, seeking a declaration of his eligible status. The question would be, who is the defendant? I suppose the answer could be a state official in charge of elections, but there would to be a real "case or controversy," so Cruz could really only file such an action if there was some reason to believe that the official would likely bar Cruz from the ballot.
Methinks Trump should stick to his area of expertise, and stop handing out "free legal advice" (e.g., engaging in the unauthorized practice of law)
Actually Cruz can go to court to request a “declaratory judgement” preemptively on a matter that he may be threatened by future lawsuits.
wrong dude.....Cruz would be the defendant if there was anyone on the planet with “standing” to be the plaintiff. And there isn’t.
Not even Alan Grayson, tho we’re not sure he is from this planet.
It’s called a declarative court statement and is common.