Need help to approach tax filing services..!!

Hey, I was in abroad for last few months. I missed my tax payments when I was away from home. Currently, I'm planning to start a small business near Toronto. I need to pay what I owe before starting my new career. I'm not aware of the formalities of tax payments, and I don't know whom I should approach to get assistance to pay my debt.

I found several firms providing Tax payment plans near Toronto. Can I approach such firms to clear my debts? Does anyone know what all services are offered by such firms? Have you ever gone through such a situation? Please let me know the details. Any help would be highly appreciated.