MSW

A Master of Social Work is a credential that you will often see for counsellors/therapists and is a good couple of letters to notice as many extended health care plans will cover sessions with an MSW. 

It is good to know that social workers are unable to provide a mental health diagnosis or prescribe medication. However, social workers are trained in issues around mental health, so if your therapist suspects that a formal diagnosis or medication might be helpful to you, they might suggest you connect with a psychiatrist.

RSW

A Registered Social Worker is an individual registered with the Ontario College of Social Workers and Social Service Workers (OCSWSSW), which is a regulatory body that ensures ethical practice and protects public interest. If you ever have a concern about a social worker's behaviour, this is who you would reach out to for support.

Coverage

If you have extended health benefits, I recommend that you review your plan as most insurance providers cover sessions with an MSW, RSW.  

If you do not have extended health benefits, working with a Registered Social Worker means that you might be able to claim sessions as part of your medical expenses when you do your taxes.