It’s pretty clear in ANH that Bail Organa was supposed to get the plans. And we know he’s in a caméo sequence with Mothma when the mission is discussed, so I guess it was Captain Antilles job to get the plans so that as a diplomatic ship he could avoid further Imperial investigation… but Vader couldn’t care less about diplomatic regulations and attacks the ship. The fact is that Leia was also supposed to meet with Ben and ask him to get involved. We might get some more info about a “hidden Jedi Knight who could help us”.

[I also wouldn’t mind at all a scene with the Imperial Senate, since we’ve never seen the Senate in the Imperial era; could be quite fun to see PT and OT visual styles colliding in one sequence]