I had a anterior cervical spine fusion of c6/c7 three years ago and I'm still having significant neck pain. Is this normal?

Possibly. The surgery will decompress the spinal canal and foramen (area where nerve roots exit). So while it can help with neuropathic pain, a number of musculoskeletal pain generators exist. If it is a problem, seek care.
Evaluation time. Significant pain is something you should evaluated, whether it is from a previous spinal fusion or not.