Each province has its own pre-assessment program, but each of them has defined its own way of assessing foreign-trained physicians. It's difficult if you're an IMG and you're interested in applying to multiple provinces. It gives them their best possible chance: the more programs they apply to, the more universities, the better chance they have. However, if they're assessed in B.C., for example, that's an enormous amount of investment of their own time resources. You have to be a resident of B.C. to be assessed there so they can't realistically apply to any other province. Likewise with Quebec: you're assessed as an IMG in Quebec, and it's difficult to apply outside Quebec because you have to be a resident of Quebec to be assessed in Quebec. Likewise in Ontario.
So we're really pigeonholing the IMGs provincially and not allowing them the flexibility to apply to positions across the country, which reduces the selection and reduces the opportunity for the applicant.