You cannot freely move your Mii. Wii Sports Resort Basketball (3-on-3 Pickup / 3-Point Contest) uses fixed camera rails and auto-positioning.
Other Resort sports (Swordplay, Wakeboarding, Archery) give direct avatar control. Basketball is a simulation-lite—you're the coach/point guard, not the whole team.
Master the pick-and-roll timing; that's where the skill lives.