Green’s Dictionary of Slang

1. (US) to sing.

1905

F. Hutchison Philosophy of Johnny the Gent 22: Them guys that separate themselves from a five case note to [...] hear a mob o’ Dagos canary.

2. of a criminal, to confess, to turn state’s evidence [canary n.¹ (4c)].

1949

Monteleone Criminal Sl. (rev. edn).

3. (US) to work as a band vocalist [canary n.¹ (4e)].

1938

W. Winchell On Broadway 24 Nov. [synd. col.] Ross Maclean’s canarying at the New Yorker.