First of all No one on this forum is an "Expert", "Lawyer" or "Consultant".On this forum ordinary people give their point of view.Which should not be taken as provision of Law or an advise by an immigration expert.It is a forum where people learn through expeiance of one another.
For accurate information always read the information published by the Government of Canada.
If you have been asked by the Manila Health Authority to undergo a medical exmination, it might be their policy to do so for people who re enter this country after visiting countries abroad.
The objective may be to rule out infections that you may have been effected with durng your visit abrod.This may also be a precaution to ensure that other citizens are not effected if you are a carier of a particular condition.
So attend the scedule Medical check, it will be in your own interest as well as good for others. good luck.