Hey GeeO, my husband and I are living in Canada as well and we just submitted my document a week ago.
We had our medical exam done, attached it with the document and sent it to Mississauga. However, the result of medical exam was sent to Ottawa by the doctor since all the medical exams taken in Canada are sent to Ottawa and are registered there so the other CIC offices around the world can see them online.
I wrote "CPP - Ottawa" on the Option C form, but my doctor told me that he needed the office name outside Canada because he can't write down "CPP - Ottawa". I don't know if he needed to fill the form up online, which may have been the reason he couldn't choose CPP-Ottawa, but he kept saying that I had to choose one office outside Canada and I ended up telling him to write "Buffalo", which has been closed. However, as I mentioned above, it doesn't matter which office the doctor writes because the result of the medical exam is sent to Ottawa first anyways.
You'll send the other documents to Mississauga and the visa officer will send them to CPP-O or the other office you belong to, like OhCanadiana posted.