I'm in New Brunswick and used a lawyer since I wanted the custody stuff deal with too. My best friend is an RCMP officer and told me that if my ex took my son and refused to return him, we would need to wait for an emergency court order to get him back.
You can file online. I know NB has a family law website with the forms you need. My lawyer was awesome though, I paid $500 (through a payment plan) to him and my ex got stuck with the rest of my fees. He knew I would end up with back support and my ex was garnished through the courts.