All songs performed by New Directions in the Nationals competition are said to be Finn's favorites according to his mother Carol. That is reinforced by Sam raising drum sticks at the end of the team'a performance.
The three songs that were sung by the New Directions that were said to be favorites of Finns were in fact three of Cory Montieth's favorite songs.
Skylar Astin (Jean Baptiste) is good friends with Lea Michele (Rachel) and Jonathan Groff (Jessie) since they all worked together in the Broadway musical "Spring Awakening". Another good friend and "Spring Awakening" cast-mate, Phoebe Strole, had appear in Glee (2009) earlier in the 5th season. Jenna Ushkowitz (Tina) had also joined the cast of "Spring Awakening" in 2008 as an understudy.