Bowling. Given the physical requirements for bowling such as trunk flexion and swinging of a heavy object in one arm, your fusion should be fairly well healed before return to this activity. Lumbar fusions generally require 3 months for early signs of fusion that are needed for return to normal activity.
Varies. This depends on region of fusion, why fusion was done, levels involved, how fusion was done & if instrumentation used & whether there are factors like smoking that may stop or slow a fusion. How deconditioned or rehabilitated you are via physical therapy plays a role. If a neck fusion, could be as early as 3 months & for the lower back at least a year. For scoliosis surgery 1 year if fused.