It's always a good idea to have more volunteer experience if you have the time to do it and it would strengthen your application. I think your experiences are relevant to social work practice, and your research experience is definitely an asset. Knowing social work vocabulary will make it easier to understand the course-work so I would recommend becoming more familiar with the vocabulary for your own understanding.
I don't think you will have any trouble understanding the curriculum or doing well in the program with your communications degree.
I would suggest applying for post-grad BSW programs because it will open up more options for MSW programs. However, I would apply to an MSW program and have the post-grad program as your back-up. A lot of BSW programs will have placements so you will get more volunteer experience that way.
Mswnewbie got a reaction from _Nomad_ in Canadian MSW Applicants 2018