You dont need to worry about your weight as long as you dont have any other problems that come with it ( that is for your own good only). Even if you have high BP or heart problems, it is in no way a threat to the people of canada (unless you decide to kill other people because you are going to die).
Medical examination only checks for communicable diseases such as TB, HIV, Hep C and other sexually transferable diseases. If you dont have any of these, it wont be a problem.
Relax