The chorus is a variation of the often-used hymn tune, "Lasst Uns Erfreuen," which Ralph Vaughan Williams introduced in the English Hymnal in 1906. You may know the melody as "All Creatures of our God and King," "Ye Watchers and Ye Holy Ones," or "From All the Dwell Below the Skies." If you think you know the tune, be careful. The second "Hallelujah" is cut short, and isn't quite like the hymn tune.
"Sugar pie" is a French Canadian concoction - like pecan pie without the pecans.