As near as I can figure, WHAUR WILL WE GANG is an original song written by band members Mike Katz, Karine Polwart, and Alan Reid.

I found a brief quote in the Honolulu Star-Bulletin and I added a few words that I heard myself in a sound sample from Barnes & Noble:

[MALE VOICE:] Let's go tae some Polynesian
Island where it's never freezin'.
Lovers wed there ev'ry season
By the Coral Sea.
[FEMALE VOICE:] But I'm a' peely-wally white
And my bikini's gettin' tight
And you are no' a bonny sight
In trunks a size too wee.
[CHORUS:] Ee-o the heerio,
Whaur will we tarry-o?
If we have to marry-o,
Whaur will we gang?