Asked if Cherry-Evans was also applying pressure to starting halves Thurston and Cronk, Sheens added: "He is applying enough pressure to keep both boys on their toes, that's all I will say there.
"That is almost what you are saying but he has certainly got them looking over their shoulder and that is a great thing as is in every position. No one is really comfortable."
Asked if Cherry-Evans had been the form halve of the squad, Sheens said: "No, I wouldn't make that comment.
"I think all three, like they have been all year, have been the three best halfbacks.
"In my opinion they have been the three best halves in the NRL and you look at where they finished in the Dally Ms.
"Cooper won it and JT and Daly were neck and neck.
"They all made semis together.
"Daly went a little further but at the end of the day you can't split those three and that is a blessing.
"For me, it is a headache and a blessing.
"There is no squad in the World Cup at the moment who can afford to lose a halfback and when I say we can we have a very good option there if three goes back into to.
"Not too many others can say that, in fact no one else can say it that I know of.
"That is the strength of our team."
The right centre position and the decision of whether or not to play Paul Gallen at prop are the other two contentious decisions to be made along with the make-up of the bench.
Brent Tate and Jarryd Hayne are in the fight for right centre while Gallen's fate will decide the make up of the pack and the bench.
Asked if we would see what Sheens rated Australia's top 17 this week, he said: "I wouldn't suggest it is my best side, no.
"This week I can still play a little bit with the bench.
"When we name the 13 it will be close to what I think is our best. But again there is still a little bit of football to play."
THE 20 MAN AUSTRALIAN SQUAD FOR GAME AGAINST UNITED STATES IS:
Cameron Smith (c), Paul Gallen (v/c), Greg Bird, Darius Boyd, Daly Cherry-Evans, Boyd Cordner, Cooper Cronk, Andrew Fifita, Jarryd Hayne, Greg Inglis, Brett Morris, Nate Myles, Josh Papalii, Corey Parker, Matthew Scott, Billy Slater, James Tamou, Brent Tate, Sam Thaiday, Johnathan Thurston.
- The Daily Telegraph