The Tipperary team shows one change from the semi-final victory over Limerick with Evan Sweeney returning from injury at corner-forward to the exclusion of Ryan O'Dwyer.
Newport's Conor O'Mahoney, who came on for Philip Maher in Sunday's loss to Galway in the All-Ireland SHC quarter-final, lines out at full-back.
Toomevara's Francis Devanney, another member of Ken Hogan's senior squad, captains the side from the centre-forward position, while Sweeney and Darragh Egan are other senior players in action.
Gaynor, a high profile manager with Clare and Tipperary during the 90s, has opted for a more background role with this U21 side with Tom Fogarty taking charge of the coaching duties.
"I like working with young players and this year offers an opportunity to be part of something special," he said.
"It's good to see young players coming through at this level and if there is anything I can contribute at this level, I'll gladly lend a hand. Even though I'm not training the side, I'm still enjoying the experience." He plays down talk of a three-in-a-row.
"If we're to win the Munster title, we'll have to play to our optimum level. The seniors travelled to Cork for the Munster final and came up against a very strong Cork side. Cork are always dangerous at home and it will be no different tomorrow night.
"The lads will have some experience of playing in the Park they would have lined out there at minor level. It's as good a ground as Thurles so that shouldn't affect our play although there obviously will be a bigger Cork crowd as they're playing at home."
Gaynor adds that everyone involved with the squad is conscious of the heartbreak of last Sunday's senior defeat to Galway and would like to give the Tipperary public something to cheer about in tomorrow's clash.
"We know the supporters are anxious to see the county achieve something for the season and we're all anxious to put something on the roll of honour for the season. We know too Cork are going for a clean sweep of titles having already won the senior, minor and intermediate provincial titles."
TIPPERARY (U21H vs. Cork): P McCormack (Thurles Sarsfields); J O'Dwyer (Killenaule), C O'Mahoney (Newport), B Hanley (Lattin-Cullen); C O'Brien (Éire Óg Annacarty), N Teehan (Gortnahoe/Glengoole), T Collins (Ballina); S McGrath (Ballinahinch), W Cully (Thurles Sarsfields); T Fitzgerald (Roscrea), F Devanney (Toomevara Captain), D Egan (Kildangan); E Sweeney (Loughmore-Castleiney), T Scroope (Burgess), P Shortt (Upperchurch-Drombane)