Finally, some Great Big Sea on the Internet. Although I can't make out most of the lyrics, I have figured out chords for the song. It's pretty simple, only four chords: G, A, Em and D.

Start off with quick changes from G to A to Em ^{listen to the album
for the proper rhythm}.

During the verses:

" ^Em There's a cute little lass and her name is Mari-Mac ^D And make no mistake she' a girl I'm gonna track ^Em A lot of other fellas try to get her on the back. But I'm ^G thinkin' they'll ^A have to get up early ^Em. ^Em Mari-Macs mother's makin' Mari-Mac marry me ^{D once hard
and then mute it} My mother's makin' me marry Mari-Mac^{a few rapid D's} ^Em Well I'm gonna marry Mari cause Mari's takin' care. Well ^G I'll be feelin' ^A marry when ^Em I marry Mari-Mac. The rest of the song follows this same progression but it get's much faster so listen to the album and you'll figure it out much better than I can describe.

Great Big Sea - Mari Mac