3rd Test starts in a few hours - it is now do or die for England. I do agree that they should look at including another "bounce" bowler in their XI - Finn would be my choice. I hear that Bresnan is back to full fitness too, so will come into contention. It will be interesting to see whether they do go in with 4 specialist pace bowlers - given Swann has not impressed so far I'm sure it is something they will consider. Rankin may be an option, but has no experience at this level, while Tremlett didn't really impress in the 1st test (his figures were ok, but he just seemed a bit slow).
If they do opt for 4 pace bowlers I don't think there is any reason to include Stokes - he is a promising young player, but I think both Ballance at Bairstow are better batsmen at this stage (and England need as many runs as possible!).
I don't expect any change for Australia, as I understand Harris has been passed fit. Lyon looks set to start again (instead of Faulkner) - he has bowled pretty well so far, and Australia won't want to change a winning combination. Johnson has been the key for Australia so far - I felt he was starting to show signs of fatigue near the end of the last test (allowing the England batsmen handled him comfortably), but he has had some success at the WACA before.
EDIT: Only one change for England, with Bresnan in for Panesar. Australia are unchanged.