This study examined the effect of choice on EFL learners' task engagement. Twenty-four Thai university students completed two opinion-gap tasks. In one, they discussed and agreed on three items among given options (+constraint). In the other, they discussed and agreed on three items among the options they generated (-constraint). Spoken interaction and questionnaires were analyzed for behavioral (time on task, words produced, turns), cognitive (negotiation of meaning and form, self-repairs), social (overlaps and turn completion, backchannels), and emotional engagement (anxiety, enjoyment), based on Philp and Duchesne's multifaceted model. The -constraint task had positive effects on all the cognitive engagement measures, but only one of the behavioral measures (turns) and one of the social measures (overlaps). Learners reported higher anxiety and enjoyment in the -constraint task. The findings highlight the interrelated multidimensional nature of learner task engagement while suggesting pedagogical implications and avenues for future research.