Green’s Dictionary of Slang

(orig. US) positive, enthusiastic, aggressive.

1978		H.R. Haldeman Ends of Power 220: 1971 saw the rise of [White House counsel Charles] Colson as Nixon’s ‘can do’ man.
2000		Indep. Rev. 25 Feb. 13: Max’s icy ‘can-do’ attitude.
2001		Week (US) 8 June 25: Dressed in loud Hawaiian shirts and ‘armed with can-do moxie’.
2013		K. Sampson Killing Pool 223: I give him my best, can-do front, but fuck that.