Merthyr rose to the top of their part of the draw after fending off the likes of Ynysybwl, Pentyrch and Tondu in earlier rounds before disposing of Whitland 19-3 in the semi-final at Bonymaen at the beginning of March.
Bonymaen waded through notable opponents in Pontyclun, Bedlinog and Bridgend Athletic before a 23- 14 victory over Bedwas in their semi-final at Merthyr on the same weekend.
"The final is the climax of the season for these teams, just as any cup final at the Millennium Stadium should be," said Welsh Rugby Union Community Operations Manager Peter Owens.
"The competition this year is 30 per cent bigger with each of the 12 District Youth Unions nominating three of the best teams in their District instead of two, making the achievements of both Bonymaen and Merthyr in reaching the final this year all the more special."
Merthyr youth field a side lead by hooker James Howe, who is flanked in the front row by giant prop Richard Powell - brother of Cardiff and Blues back row Andy - and also featuring Coach Craig Dummett's son Mitchell at inside centre.
Bonymaen Coach John Tregembo has named flanker Richard Brooks as his captain and both teams will be giving their players, who can range in age from 16 to 19-years-old, a unique taste of Millennium Stadium atmosphere with the fixture returning to the capital ground after a one year absence.
The second half of the Millennium Stadium community rugby double-header features the Worthington Welsh Districts Rugby Union which kicks-off after the Webb Ellis Youth Cup is lifted (KO 3pm).
This game will be hotly contested between two district sides who have impressive recent form in the competition.
Bryncethin and Cambrian Welfare meet in the 34th Final with Cambrian looking to emulate their 1997 Arms Park victory and lift the trophy. Bryncethin play their third consecutive final with one win in 2006 and a loss, last year, to their name.
"Players don't get to experience huge games like this at the Millennium Stadium many times in their playing career, if at all, and it will be a huge honour to all those taking part," said Secretary of the Welsh Districts Rugby Union John Owen.
"There should be little between the two sides and we can expect them both to make a real game of it as they attempt to ensure a long season ends with the glamour and glitz of lifting silverware at the Millennium Stadium."
Webb Ellis Youth Cup Final (Kick-off 12 noon, Millennium Stadium)
BONYMAEN YOUTH: Chad Punchard; Christopher Hoppe, Ashley Bowd, Paul Davies, Dean Williams; Richard Williams, Thomas Bevan; Luke Myatt, Rhodri Clancy, Richard Murphy, Richard Sturgess, Daniel Fala, Richard Brooks (Captain), James Bija, David Leonard
REPLACEMENTS from: Jordon Griggs, Leon Gallagher, Adrian Cousins, Alex Stubbs, Luke Griffiths, Jonathan Vaughan , Simon Davies, Joe Milan, Gareth Jenkins
MERTHYR YOUTH: Tom Griggin; Bleddyn Rees, Michael Conway, Mitchell Dummett, James wood; Lloyd Hynes, Daryl Jenkins; Richard Powell, James Howe (Captain), Marcus Lewis, Aaron Harris, Creighton Rees, Lewis Ayling, Matthew Rees, Kristian Dacey
REPLACEMENTS from: Andrew Murphy, Giancarlo Howfield, Rhydian Burke, Scott Jones, Marcus Clyne, Michael Phillips, Alun Hicks
Worthington Welsh Districts Rugby Union Cup Final (Kick-off 3.00pm, Millennium Stadium)
BRYNCETHIN: Mike Richards; Richard Handly, Chris Wiliams, Jamie Davies (Captian), Russell Johns; Andrew Veasey, Lloyd Jenkins; Huw King, Neil Hopkins, Steve Walters, Jonny Smith, Kevin Baldwin, Mark Thomas, Andrew Bayliss, Paul Evans
REPLACEMENTS: Gareth Pearce, Rowan Hobbs, Rhys James, David Bayliss, Leighton Jenkins, Peter Puaca, Tony Stevens
CAMBRIAN WELFARE: Phillip Gowing; Jonathon Richardson, Paul Martin, Christian Ashford, Gavin Thomas; Julian Huntley, Jonathan Jones; Lee Thomas, Marc Whitford, Craig Griffiths, Damon Filmer, Kevin Lawrence, Christopher Davies, Anthony Jones (Captain), Robert Norton
REPLACEMENTS: Craig Chedzoy, Zak James, Criag Meredith, Ritchie Lewis, Matthew Jones, Mark Jones, Wayne Morgan