This is no flag-waving, war-themed short like many others made at this time. This is about a pushy agent (Daffy Duck) performing a series of overbaked musical numbers in an attempt to interest a producer (Porky Pig) in his client (Sleepy LaGoof). Why "Yankee Doodle"?
The title is meant to evoke the multi-talented showman,
George M. Cohan, who had recently been played by
James Cagney in
Yankee Doodle Dandy (1942) (1942).
Also, the phrase "Yankee Doodle" could not be bad for business in wartime.