Did you actually read the article that you linked? Halfway through it states this -

"Cruz, as an employee of the government, will use the exchange to choose his employer-provided insurance. Iowa U.S. Sen. Chuck Grassley pushed through an amendment on the Affordable Care Act that requires members of Congress to obtain their coverage via the exchanges. Congress pays most of the premium. But Cruz won't be getting any extra benefit under the Affordable Care Act that a member of Congress wouldn't have gotten before the ACA became law."

Doesn't sound to me like he has a choice, unless I am reading it wrong??