FWIW, here's what Wikipedia has to say about Dylan's album "Good As I Been To You", on which "Canadee-i-o" appears:

Though Dylan is credited with all of the arrangements, several arrangements clearly belong to other artists, including the Texas songster Mance Lipscomb. A number of publications, including Folk Roots, criticized the album for making this error. Lipscomb's posthumous oral biography, I Say Me for a Parable, edited by Glen Alyn, claims that Dylan listened to Mance play backstage at Newport in the early 1960s and then later took the stage and sang Mance's songs as his own.

and

The inaccurate song credits created some controversy for Dylan. Nearly half of the songs were incorrectly credited, and in one case, Dylan faced legal action when Australian folksinger Mick Slocum sued Dylan's music publisher over the arrangement credit in "Jim Jones." Slocum recorded his arrangement with his band, The Original Bushwhackers, in 1975, and Dylan's publisher was forced to concede their error

While saying "the original album notes incorrectly credit all song arrangements to Bob Dylan", Wikipedia credits the arrangements of "Frankie and Albert", "Canadee-i-o" and "Arthur McBride" to Mississippi John Hurt, Nic Jones, and Paul Brady, respectively. I don't know if the album was ever reissued with changes to the liner notes.

I wasn't very familiar with "Canadee-i-o" at the time, but I remember when I first heard Dylan's version of "Arthur McBride", my impression was that it was, note for note and phrase for phrase, so similar to Paul Brady's that it seemed like . . . cheating, somehow. A ripoff, if you will.

So, in response to Joe Offer, I would say that this is not just a case of "anyone can sing a song however they like." This is a very prominent artist "borrowing" the work of less prominent ones, and not crediting his sources. It's wrong.