Hey Canadianinlove,
My husband didn't receive a letter from the POS office when the file got transferred. I noticed that a week after the file was transferred my E-cas changed and there was a section for "permanent residence application" and under it, it said "Application received". The only letter he got was the one received a month after the transfer stating the steps that he needed to take to finalize his application. Hopefully, it will be the same for you guys.
Also, the mississauga office just views the sponsor's application and material... The POS office would be the one to request the medical if he hadn't done it as yet.
Hope that helps!