fifty-fifty draw 50/50 draw, 50-50 draw, 50-50 raffle, 50-50 raffle draw DCHP-2 (October 2016)
n. — Games
a charity lottery in which the proceeds are split equally between the winner and the charity.
Type: 5. Frequency — This is the preferred term in Canada (see Chart 1), where it also occurs most frequently. Low frequency of fifty-fifty draw in other countries can be largely attributed to the equivalent term fifty-fifty raffle, which is especially popular in the US.
See also COD-2, s.v. "50/50 draw", which is marked "esp Cdn".
Images:

Chart 1: Internet Domain Search, 4 February 2014
Chart 2: Internet Domain Search, 4 Feb. 2014