I don't believe these two have ever worked together, have they?
Gaghan, known primarily for his skills as a screenwriter (for which he's won an Oscar), last directed the political Syriana (which starred George Clooney and others) for the big screen (although he also directed a TV movie for NBC last year, called Metro, according to his IMDBPro page).
No word yet on plot for Candy Store, or what roles Denzel and Brad are being considered for.
The project isn't even listed on IMDB yet – although I'm sure that'll change soon enough.
THR just describes it as "a "two-hander" crime thriller with meaty roles for the two main characters." That's it!
A Google search revealed lead to the website for a production company called Flashlight Films, which refers to Candy Store as an "original international espionage thriller." Although I'm not certain what their exact relationship is to Gaghan.
Up next for Gaghan is the the Will Smith/Jaden Smith sc-fi adventure movie, After Earth, which has M. Night Shyamalan directing. He co-wrote the screenplay for that project.
Denzel will next be seen in the Robert Zemeckis drama Flight, this fall.