More on the chanson link. I think it definitely explains alot --- and I think in light of the history of Jersey and what is known about chansons -- the donkey is just that "a donkey" -- it is not so amazing how a chanson would appear in Newfoundland as one might think, but it does place a greater antiquity to the song:

The organized colonization of the islands around Newfoundland started at the end of the XVIIth century and was officially encouraged by King Louis XIV. Most settlers were fishers from Pays Basque, Brittany and Normandy. Merchants from Saint-Malo (Brittany) settled in Saint-Pierre and built warehouses dedicated to codfish storage. The Great Banks were so rich in cods that the explorer Giovanni Caboto (XVth century) is said to have fished a lot of cods just by dipping a basket in the water. Cod fishing was a source of dispute between the French and English settlers in North America, which turned into a succession of wars.

The Channel(Jersey) Islands acquired commercial and political interests in the North American colonies in the 17th Century. Islanders became involved with the Newfoundland fisheries in the 17th century and in recognition for all the help given to him during his exile in Jersey in the 1640s, Charles II gave George Carteret, Bailiff and governor (of Jersey Island), -- [Geroge Carteret was a very successful Pirate hunter] a large grant of land in the American colonies, which he promptly named New Jersey, now part of the United States of America.

Colonists would have came over from Jersey during this period of time, and with them brought their songs[chansons] from the Normandy coast... and even more interesting is their movement to Nova Scotia in 1713, and may explain the Nova Scotian variant, "Chanty Song" about George I (1714). I think this song much older than it appears...and may have been adapted to fit the Timberships, Donkey Engines, as well as corrupted by bawdy sailors at sea... but invariably -- A cigar is sometimes just a cigar, and a donkey -- just a donkey.

Cheers,
Brian