Early cite for Canuck

[Sam Clements]

As Fred Shapiro has recently pointed out, race-horses quite often have names early in the life of a word.

While not an antedating, at least for the derogatory name, I found

20 June, 1840  _Alton(IL) Telegraph_  4?/1(Newspaperarchive)

(An ad for a horse at stud)

<<The celebrated fast pacing Canadian Horse, CANUCK,
will stand the present season, which has commenced, and will expire....>>

Depending on how far back the career of 'Canuck' went, he certainly could have helped popularize the word.  

Sam Clements