Helo,
I've got my ECA of medicine degree done by WES, Canada.
As far as the immigration process is concerned, ECA done by WES is valid. They'd evaluated my MBBS as a 'Professional degree needed to practise in a licensed profession"
However, if you are planning to get license to practise medicine in Canada or to study higher in Canada on the basis of your medicine degree, you must get your degree assessed by MCC.
If you have these plans further, then it's advisable to go for MCC evaluation. It'll help in your immigration as well as further licensure procedures.