Based on what I could find, the trailer is 21 seconds long and features Vader choking Anakin.
It's referenced on GameSpot as Official Movie 17, but it's not on LucasArts' official Gamefront page, and YouTube searches have been typically unhelpful. It's a small bit of Battlefront history, but it's a neat one: the public's first glimpse at the awesomeness of heroes from all eras clashing. It would be a shame for it to disappear forever due to negligence.
Here is the GameSpot reference: https://www.gamespot.com/videos/star-wars-battlefront-ii-official-movie-17/2300-6140026/