There is no medical check required for a simple visitor status extension of a visa-exempt applicant.
All necessary docs for a UK outland application can be obtained while one is still in Canada. There is pretty much no reason you would have to leave to the UK at any time, only in the very tiny chance an interview is required. Of course the vast majority never require interview.
Also applying outland gives you the freedom to leave Canada for vacation as you wish, and not have to worry about re-entry to Canada and possibly having your PR app cancelled on you.
All necessary docs for a UK outland application can be obtained while one is still in Canada. There is pretty much no reason you would have to leave to the UK at any time, only in the very tiny chance an interview is required. Of course the vast majority never require interview.
Also applying outland gives you the freedom to leave Canada for vacation as you wish, and not have to worry about re-entry to Canada and possibly having your PR app cancelled on you.