Competition's rhymes with:
competitions, competitions, competitions, competitions, petitions, repetitions, competitions, dietitian's, dietitians, mathematicians, petitions, politician's, politicians, politicians', repetitions, theoreticians
Competition's sounds like:
cambodians, combating, combatting, competence, competencies, competency, competing, competitions, compton's, computations, computing, confidence, confidence's, confidences, confiding