I think that's quite unlikely for a healthy person, but the reasons for failing the MEDICAL are:
- You are a danger to the Canadian population (so if you have contagious and potentially fatal disease)
- You are too expensive for the Canadian health system to keep you alive (so if you have a condition that will require a complex or expensive Surgery in the near future or require very expensive medicine)
So long as you don't have a complicated medical condition and are not suffering from a contagious disease you should be ok!
You have probably read this already but the medicals consist of:
- Urine test (if there is something abnormal here they will request more tests - example, high sugar in urine could indicate diabetes, etc.)
- Chest XRay - they want to rule out TB (tuberculosis)
- Blood test (HIV and Sifilis) - here if you're positive for HIV then you'd probably fall into the "too expensive" category as Meds for HIV are expensive and Sifilis if you're positive then they will request more tests to make sure that you're cured and not currently infected.
- Standard check up (blood pressure, etc.) - doc will take blood pressure, listen to your lungs, prod your tummy, etc. (again anything abnormal will lead to more test, for example, high blood pressure will probably mean a visit to a cardiologist, etc.)
There really is no point in worrying about this now (unless you know you fit into one of the categories above)... If you are worried then speak to the doctor, tell him to be honest with you and tell him that you'd like a copy of the tests, that should be a good indicator for you to know if you're OK or not!
Hope this helps!