Medicals are requested depending what you are applying for and from which country you are applying. A medical must be performed by a medical professional listed as officially signed up to perform a medical for Canada immigration purposes, otherwise referred to as a panel doctor. As long as an official panel doctor that doctor does not need to be in a home country.
There is no specific type of medical but the main criteria would be that an individual would not be a drain on Canadian medical resources with some long term health condition. It would be expected existing conditions are declared and apart from a physical exam also an x- ray.
If as a result of a medical such a condition exists then someone could be deemed inadmissible , depends on the program being applied for and also what discretion a visa officer might have with an application.
Visitors for example might have a better chance of not being medically inadmissible , unless having some communicable disease, given the expectation is they would need travel insurance
