Never head of Cojanu. The others seem really good as opponents. Personally, I'd get my bum over to Tyson Fury's camp and spar with him and his brother. There's your height. Ustinov is the logical choice. Duco knows him, and he's been over here before. AND, he's ranked in one of the alphabets.
In addition, the public knows Ustinov, and there's some hype to be gained in saying he beat Tua.
In addition, the public knows Ustinov, and there's some hype to be gained in saying he beat Tua.