Here's a spitball for you. So apparently Giant makes Specialized's frames for them. The Specialized Roubaix has a max of 240 lbs. The Defy Advanced is Giant's version of the Roubaix. Ipso facto, maybe a Giant Defy Advanced limit is around 240 lbs as well.
Of course, I've ridden my Roubaix as heavy as 285 lbs and no problems as long as I have good strong (well built 32 spoke) wheels on it.