The second full trailer for The Chronicles of Narnia: The Voyage of the Dawn Treader was included on the US DVD and Blu-ray for The Diary of a Wimpy Kid, released just this week. Of course, somebody had it on YouTube lickety split.
So… that’s not a trailer “leak” exactly, but I don’t know what else to call it.
The film reaches cinemas in December. All the other info you might want lurks at the official Facebook page.