The Black and Whites defeated Highland League champions Fraserburgh to earn their place within the four-team match.
Peterhead progressed to the ultimate with a penalty shootout victory towards Inverurie Locos.
Elgin Metropolis will face Peterhead within the last of the Borough Briggs one centesimal anniversary match on Sunday.
Fraserburgh will face Inverurie Locos within the third/4th place decider within the opening match on Sunday earlier than Elgin tackle the Blue Toon to determine the winner.
Elgin ran out 2-0 winners towards Fraserburgh on Saturday with Brian Cameron netting from the penalty spot after 17 minutes earlier than Jake Dolzanski headed residence the second simply earlier than half time.
Inverurie Locos had been in entrance towards Peterhead within the different semi-final when new signing Garry Wooden headed residence after 31 minutes.
Conor O’Keefe, again at his outdated stomping floor, equalised for the Blue Toon after 74 minutes with the Balmoor males progressing on penalties.
Elgin will face Peterhead at 4pm on Sunday with Fraserburgh assembly Inverurie Locos at midday.