Pearce will name a 23-man party for the tournament in Israel after friendlies against Romania at Wycombe's Adams Park on Thursday and Austria at Brighton's Amex Stadium next Monday.
The 50-year-old admits he has between 18 and 20 names already firmly in his thoughts but wants to keep an open mind about who else might join them.
"You have to bear in mind that we have been in a qualification process now for the best part of two years, so we know who has contributed really well for us," he said.
"But the thing is, at under-21 level especially, people can come on the scene very late and I wouldn't rule out anybody at this stage.
"It would be fair to say that if I had to jot 18, 19, 20 names down on a list that I hope will be there fitness-wise, we know those.
"But as I have found out in previous years, there is always one or two people that come in very, very late - Leroy Lita in my first time out had a real late charge, got in the team and had a real impact, and various other players have done exactly the same."
One player Pearce wants available for the summer is Tottenham defender Steven Caulker, who had come back into the Under-21 squad for their forthcoming double-header but has now been called up to the seniors following the withdrawal of Rio Ferdinand.
Caulker is eligible to play from the start of the Under-21s' campaign in Israel after the two-game ban imposed on him by UEFA relating to the trouble at the end of the qualifying play-off second leg in Serbia was lifted on appeal.
Pearce said: "He is a real top professional and really wants to learn the game.
"I had the fortune to work with him not just at under-21 level but with the Olympic squad (which Pearce was in charge of last summer) as well, and the way he conducts himself and, more importantly, the way he wants to get better at his profession, is commendable.
"We are delighted he is up with the seniors and I think he thoroughly deserves that opportunity."