Personally would love to see the brave option of five bowlers but without Bresnan that is even less likely than it was already - and it was very unlikely then given Strauss' comments in his Ashes Diary to the effect that he never saw the point of a fifth bowler unless they were a genuine all rounder.
So Tremlett, Finn or Onions...I'd be inclined to say Tremlett - two reasons being that he is naturally intimidating enough that he'll still get the Pakistani batsmen on the back foot both literally and figuratively, and that he is considerably more consistant than Finn at this stage in his career, meaning that he will not exist as a release valve for the pressure created by the other bowlers.
Personally, I'm not convinced that this will be a run fest at all - England's structure has always been to build pressure on the batsman and to try and get wickets by way of poor shotmaking etc, and I don't think that this is likely to change too much regardless of conditions.