My money on Michelle Ould. If she is profesional MMA fighter then does not matter that she is a woman and is smaller. Wrestling techniques are part of the MMA. She will beat such man as Justin in wrestling. No matter how many rounds it would be like Justin wins most one.
Other rounds wins Michelle after armbar, the lever on the knee or elbow joint. Possibly after stewing or head scissors, too.
In MMA fight Michelle Ould win. KO after 15 sec. fight.
Justin Bieber vs Britney Spears - this would be very close match in wrestling, catfight or mma fight.