Hi! I'm in the same boat as you. McGill student thinking of applying next fall. I'm not sure if I will tbh, because I have another career path I'm contemplating and my volunteer experience in relation to this field is limited. You seem super well prepared, and research experience is always good. What is the research you're planning on doing for the thesis course about? I don't think it matters if it's not SLP or linguistics related, because you have some other SLP-related experience in there.
Are you sure about the UofT prereqs? It says the classes they had listed up until the changes this year will still be valid up to 2020. Here is a full list of accepted McGill classes: http://www.slp.utoronto.ca/wp-content/uploads/2017/01/McGill-University-Jan-18.pdf. I have to say that their prereqs are really frustrating. I won't be able to apply because I am missing one course, which McGill won't allow me to take because I'm not in the department of psychology.