Useful links:

Register an account with CRA https://www.cra-arc.gc.ca/esrvc-srvce/tx/psssrvcs/menu-eng.html

Make a payment to CRA https://www.cra-arc.gc.ca/mkpymnt-eng.html

Child and family benefits https://www.cra-arc.gc.ca/bnfts/menu-eng.html

Payroll deductions online calculator https://www.cra-arc.gc.ca/esrvc-srvce/tx/bsnss/pdoc-eng.html

Individual Income Tax Inquiries 1-800-959-8281

Business Tax Inquiries 1-800-959-5525

Canada Child Benefits 1-800-387-1193

GST Credits 1-800-959-1953

Canada Pension Plan (CPP) and Old Age Security (OAS)
1-800-277-9914

Employment Insurance 1-800-206-7218

Forms and Publications 1-800-959-2221