The music in the ending scene is the aria "Pa-pa-pa-papagena" from Mozart's Magic Flute. In the opera, it is sung by two lovers imagining their happy future together. This is appropriate because it plays over a scene in which Hailey is reunited with Rodrigo.
In the opening scene, the music playing is Salieri's Symphony in D Major, nicknamed "La Veneziana" (the Venetian), after both the city where it premiered and Salieri himself. It reflects season 3's new setting in Venice.
The pasta dish Alessandra serves Rodrigo is pasta nera. This black pasta gets its color from the ink of squid or cuttlefish. It is a traditional dish in Italian port cities, like Venice, but is thought to have originated from Sicily.
La Fenice, the building where Rodrigo is told to meet Alessandra, is the Teatro la Fenice - one of Venice's most famous opera houses. Its name translates to "the Phoenix," after the mythical bird who is periodically burnt to death and reborn from its own ashes. (Ironically, La Fenice has been destroyed by fire and rebuilt three times in its history.) The phoenix relates thematically to Alessandra's story; she is nicknamed "La Fiamma" (the Flame), and is in the process of reinventing herself after a long absence from the opera world.