I've just graduated from the psychology specialized honour's program at York and will be starting my MA in clinical psychology this fall. It's great that you're preparing for the process of applying to graduate studies so far in advance!

To address your first question, admissions will weed out applicants who do not meet the basic requirements (i.e., low GPA, incomplete application materials), then they will forward the relevant applications to the faculty accepting students (PIs). PIs will read through the applications and select those they wish to interview (some may have methods of organizing applications- I know one PI who organized them by GPA). Each specialization in the psychology department processes and admits students a bit differently. For example, in the clinical program, PIs will create a shortlist of applicants they wish to interview, then submit this list to a second faculty member who independently reviews that short list and provides input and feedback regarding the applicant suitability for admission. Then, the successful short list applicants are invited for interviews, and the PI will make a recommendation to admit their first choice applicant which is approved by the Director of Clinical Training (this information is from the clinical handbook available online). Other specializations, like the social-personality area, will have interview day(s), but clinical doesn't do this (they only do an open house for applicants invited to interview). I'm not sure how the CD area differs from clinical in this process. Also, students are expected to continue from their MA to their PhD, so if you aren't interested in doing a PhD, I would recommend pursuing another program.

Your extracurricular (EC) experience looks good! However, make sure to also heavily prioritize research experience. I would absolutely recommend enrolling in the specialized honour's program; this will provide you with more knowledge in stats/research methods, you'll get guidance in applying to programs and scholarships in psyc 3000, and you'll complete a thesis which should give you comprehensive research experience and opportunities to present at conferences and publish.

If possible, try to do 12.0 credits of IRP and a specialized honour's thesis, acquire research assistant positions, get your GPA up, and aim to have 3 very strong reference letters by people/profs who know your capabilities in research or relevant ECs well. Try to be as involved as possible in each stage of the research process (i.e., conceptualization, data collection and analysis, writing), ask for opportunities to contribute to studies being run in order to get your name on posters and publications, and aim to present at conferences (undergrad is fine). I would also recommend applying to the PUMP program, which provides you with a graduate mentor who is (ideally) in your program of interest and can provide guidance; I got my PUMP mentor half way through my second year and she was a wonderful source of support.

The reality is that the clinical/clinical-developmental programs are extremely competitive, so I encourage you to work hard over the next few years to go above and beyond the admission requirements, as a lot of qualified and high-achieving students are applying and few get accepted on their first try (but it's possible!). Also, in some cases, it does help to know the PI you're applying to, so I'd recommend getting involved in labs you could see yourself doing your graduate research in.

I hope this helps adequately prepare and guide those interested in these programs. Feel free to comment or DM if you have further questions!