The cross in question is catholic, the Fleur-de-Lis is probably just French decoration as the buidling was finished in 1713.

The seminary was founded by the society of the priests of Saint Sulpice named after the church of saint-sulpice in Paris, in turn named in honour of Saint Sulpicious the Pious, Bishop of Bourges (read Tours and close to Tours). Rather ironically, he is venerated in both Catholic and Orthodox churches, as he lived from the late 6th century to 644, before the great schism split the church in 1054.