VAC is: Visa Application Centres (near of your spouse country)
Your spouse have to do his\her medical before sending application.
When they receive your application on Mississauga, they will send you AOR1.
When you get AOR1 your eligibility for sponsoring start in process for Decision Made.
After DM, the sponsorship status changed to Decision Made that mean you are eligible to being sponsor.
Then they send your application to VAC (the centre near of your spouse country) for processing your sponsorship eligibility.
After that, they send you SA (Sponsor approval) that means you are eligible for sponsoring.
Then, maybe you receive AOR2 for confirming you application received to VAC maybe not!
During this part on ECAS the permanent resident status changed to In Process.
After time processing you will get PPR (PassPort Request) that means you have to clean everything for your spouse coming
If you didn't the medical before sending application, they will ask you during the process to send it to them but it could make the time process of your application more longer than usual. Of course not a couple month but could be a week to 3 weeks.