The "chaunt" contrast, pointed out by Dead Horse, is a very good argument that O'Grady's "shant" meant something different. However, not necessarily.

First, calling the rowing song a "chaunt" may be significant itself. True, "chaunt" might just mean "song," used to be poetic. But has anyone else gotten the feeling that writers of the time used "chaunt" when they wanted to suggest certain connotations not carried by generic "song"? "Chaunt" may have been closer to "chant" -- the connotations being monotonous or repetitious (not "tuneful") singing. Why are there many references to "the Negro's chaunt" if not to somehow particularize the style of what Blacks sang? I believe "chaunt" may be a way of referring to a work song.

Second, the contrast in spelling may be explained (not rationalized, I swear!) if one considers he was using "chaunt" as a proper, established word whereas "shanty/ing" was new/dialect. To presume he would spell both with "ch" is to presume the author makes an etymological link between them, which is not necessarily the case (though he may have realized that they "sound good" together, as part of the play of words).

This was an environment where much was knew, and the French was blending with English as a new language was developing. O'Grady had come from Ireland a few years earlier. His poem wants to capture the colour of local stuff.

Lighter wrote,
A "shanty song," to an audience that had never heard of a "sea chantey," could only have meant a song somehow associated with a wooden shanty. In this case, a song sung by lumbermen on the way to their shanty.

Had the audience heard of "shanty," the hut? At the time, perhaps no one had heard of a "sea chantey." But if "shanty" were the term for a rowing/work song, unfamiliar as it may have been, I think O'Grady could have used it.

O'Grady wasn't necessarily addressing a large, international audience, nor was he necessarily subject to a big publisher's "good sense" of what a broad audience would have been expected to understand. It may have been that O'Grady was playing with local terminology because it is what he wanted, what struck him, and he was able to do it his way because it was a minor publication. He was a farmer who had written poetry about stuff he'd experienced in a new land.

Bio notes about O'Grady, here:
http://biographi.ca/009004-119.01-e.php?id_nbr=3585

The lack of quotation marks around "shanty" -- which would suggest it was an unfamiliar term for a boating song -- is compensated for by the *phrase* "shanty song" (where "song" brings the clarification).

To summarize the idea of this post:
O'Grady was in a linguistic environment where blending and switching back and forth between French and English was great. New terms were emerging, and I think he may have been using one of them, although the in-flux nature of it all makes it unclear.

My current opinion on the origins of the word "chanty" are that it is somehow *both* from French and English. That is, it came from a cultural setting in which English was used with knowledge of French sensibilities and French was used with English sensibilities -- what one might call a true "Creole" environment. The Francophile areas of New Orleans, Mobile, etc would be likely breeding grounds for that. Yet this O'Grady example forces me to consider that Quebec could be another area like that...and even if it's not what happened, it provokes me to think of the type of processes. Case in point would be: why "shanting" and not "shantying"? Even if, say, New Orleans is the source, we have that issue or grammatical forms possibly being confounded with misused/mispronounced foreign words (e.g. "chant" versus "chanty-man").

continued...