With mandatory challenger Hughie Fury having this week pulled out of the fight citing a back injury, Parker's management sought a swift replacement for the promotion in Auckland on May 6.
They have revealed Parker will face the lanky Cojanu, 30, who has won 16 of his 18 fights, including nine by knockout, and is ranked 14th by the WBO.
The holder of the WBO Asian Pacific title, Cojanu represents a significant step down in class from the unbeaten Fury, who was the No.1 ranked challenger in the division.