Alternatives to Cooper would be Amor, Walmsley, Huby, Lynch, Taylor, L Burgess. There are also a number of players who's claim is as strong as Coopers IMO, such as Crosby, Scruton, and England.
The Tomkins Hardaker dilemma is interesting, on the one hand it's great to have the issue of two class fullbacks, we've been conditioned over the last 40 years to thinking we have to shoehorn every class player into the team which results in players playing out of position. Australia don't have any qualms about leaving class players out of their squad and neither should England, Terry Lamb and Cliff Lyons couldn't get a look in at half back during the 80s. Patten, Zillman Bowen, even Haynes been left out because of Slater and Inglis presence as full backs. England shouldn't feel that they've got to compromise the structure of the whole team to accommodate a player even if he's as good as Tomkins or Hardaker.
Fwiw, here's my selection for the game Vs Australia,
Hardaker, Burgess, Watkins, Shenton, Hall, Widdop, Smith, Graham, Clarke, G Burgess, Westerman, Ferres, O'Loughlin. Subs: Farrell, Whitehead, Hill, T Burgess
The Ausies will be expecting Tomkins to play and will practice for him being at the back, they'll prepare for his unique style of kick returns and they'll base their kicking game around his perceived weaknesses. Hardaker is a different proposition altogether and whilst not unknown to Australia they will be no where near as familiar with him as Tomkins and won't practice for him being there.
In much the same way I've gone for Burgess over Charnley, totally different players in returning the ball and defensively, again the Ausies will practice to play on Charnleys perceived weakness under the high ball and will plan on putting him under pressure instead of going to Hall on the opposite wing. Burgess is 6'3" or 6'4", is much better than Charnley under the high ball and returns it out of yardage with far greater efficiency than Josh Charnley.
Only two small changes but the kicking game plays such a huge part in Rugby League, especially Internationals where territory is at a premium. If we can affect the Ausies kicking efficiency without losing any quality then we should do so, on such fine margins do Test matches turn.