Green’s Dictionary of Slang

the male or female genitals; thus (US gay) play canasta, to ogle other men’s crotches.

1951		D.W. Cory Homosexual in America 112: The obvious crotch is the basket, or sometimes the canasta.
1966		Trimble 5000 Adult Sex Words and Phrases.
1972		B. Rodgers Queens’ Vernacular 27: the overly emphasized bulging outline of male genitals [...] canasta. [Ibid.] 18: looking at crotches [...] playing canasta.