forget the medical exam date, you have a valid CoPR till 2018-APR-13.I visited physician on APR 6th 2017 but my visit date is blank on my med exam, however it says that results were transmitted to CIC on APR 13th 2017. My COPR expires on APR 13 2018 that's one year from the date meds were transmitted to CIC. In this case is my med date APR 13 2017 or APR 6th 2017. COPR document was accompanied with additional information which only states that applicant (myself) should enter on or before COPR document expires APR 13 2018 but there's no mention of meds expiration date.
Disclaimer: I am not planning to wait until last day to land in Canada, however, there are a few things to wrap up before I do so and it would be wise of me to know what exactly is the expirate date.
http://www.cic.gc.ca/english/immigrate/provincial/arrival.asp
http://www.cic.gc.ca/english/helpcentre/answer.asp?qnum=748&top=22
you have till 2018-APR-13 to land, once you CoPR expire, you are no allow to exit Canada till you PR Card arrives.
once you land and meanwhile your CoPR is valid, you are allowed to go out and enter to Canada, by land using private vehicle, if you have a valid US Visitor Visa.