Three-dimensional (3D) underwater sound propagation in a submarine canyon is investigated with a numerical model and a dataset collected in a towed source experiment. This study emphasizes the impacts of seafloor bathymetry and sediment properties, which may alter the strength of 3D sound reflections from canyon seafloor. Specifically, the numerical model is utilized to analyze the sensitivity of seafloor morphology and sediment types affecting sound propagation in the canyon. The acoustic data reveals a canyon focusing effect, and the numerical model successfully reproduces the location of the focal area and confirms the focusing effect caused by the canyon bathymetry.