Due to the stellar condition of the Brachylophosaurus finds being unearthed in the past decade there's plenty of investigative work going on. Dr. Robert Bakker explains some of it in this clip about Leonardo found here. Additionally, Bakker is interviewed here about duckbills, including Brachylophosaurus. A few clips I can post here from Youtube include a tour of the model of Leonardo:
A tour of his exhibit at the Houston Museum of Natural Science:
And a video article on mapping the dinosaur's insides:
Why so much Leonardo and so much Robert Bakker? The answer is because Leonardo is housed at the Houston Museum of Natural Science where Dr. Bakker is the curator of paleontology!