Well, Bioware's hint is the VGA trailer. If it's not Mass Effect 3, then I don't expect the next cover to be ME3.
Hm. If it seemed legitimate, I would think we would have seen it on many gaming news sites. If you can find information about it, I'd appreciate a link.
This is what I am talking about:
http://blackmesaresearchfacility.com/index.php
http://www.youtube.com/watch?v=ViLbPHX6LL8&feature=player_embedded
Back when it appeared on the internet a lot of gaming sites were commenting on it whether it was a viral website for Half Life 3 or Episode 3 or fan made. I don't know what conclusions they made.
Edit: There is no headcrab on that video, however it shows G-Man.