You must submit your Medical report along with all other documents while applying for E-APR. Which means, once you get the ITA book an appointment with IRCC approved panel physician and get it done.
Upfront medical: Getting your Medicals test done before receiving an ITA.
Other one: Getting your Medicals done after you received your ITA. I would advise to apply for medical after getting ITA as Medicals are valid only for an year.
AOR means, once you submit the complete application along with the fee, you’ll get Acknowledgment of Receipt (AOR).