Here is David Livingston-Lowe's reply

Date: Tue, 10 Jul 2001 23:50:29 -0400
From: D. Livingston-Lowe <dlivingston-lowe@attcanada.net>
To: George Seto <af221@chebucto.ns.ca>
Subject: Re: Young MacDonald
 
A Sheòrais chòir,
 
Rinn thusa obair eireachdail air an òran seo mu thràth! I'm not sure I could come up with any better guesses than you have already.
 
While you don't want to give up on the possiblility of recovering the hidden Gaelic in this macaronic song, it is also possible that they are just nonsense vocables common enough in both English and Gaelic song. Or maybe they were, or resemble, real Gaelic words but are only loosely based on them (vocables again).
 
I can think of a time I heard a popular singer from Nova Scotia (who I won't name) sing a 'Gaelic' song he thought he knew well from youth. I'm sure that he did know it from youth, after a fashion. But the words were nothing to him but jibberish. Given that caveat, however, it may just be possible to speculate on some of the Gaelic roots of these sounds.
 
Your 'Aye, (an) gràdh a tà leam' / 'Aye, (the) love that I have' is a great speculation and I can't come up with anything better. If the -tt- weren't there, I might also have thought 'Aye, an gràdh is àill leam' / 'Aye, the love I love best (prefer) or 'Aye, my favorite love'. But the -t- is there and doubled at that, so maybe your guess is better.
 
Huki wari. Hmm. I like your 'Thug i'. I wonder if the w is a broad l, giving us a word that sounds/looks like 'laraidh', or maybe even 'làr i'. Cuir mu làr = abrogate/neglect. Would "Thug i (m') làr e", she forgot about him, be possible. Pure speculation on my part.
 
Thisakerry. Shìos an ?
suas learchin. Suas (an) leargann? Suas (na) leòidean. Leòidean is the pl. of leathad. Non-native speakers often hear the neutral vowel followed by a consonant as having an -r- quality, because their only comparison is the English of England (e.g. taod sounds a bit like turd as pronounced by an English person to someone without much Gaelic.
 
meen is likely mìn
goya - I wonder if it might be bridheach, or even the -y- representing a slender -r-?
 
Anyhow, those are my thoughts for tonight. If I have a chance later this week, I'll give it another crack. Have you tried Jim Watson? I doubt there is anyone more qualified in Canada to speculate on this.
 
Is mise le meas,
Dàibhidh.