There are probably three different ways in which you might tackle those problems. The first might be with oversight of the actual impact assessment process. There's a decision that has to be made about the committee, or whatever structure would be appropriate in the Canadian context, that would oversee the process and set the parameters of the impact assessment. There you may opt for a model that gives you a range of different stakeholders.
In terms of the assessment team itself, the key there is in the members' expertise in the subject matter. You're going to need someone with expertise in economics assessment, someone with expertise in human rights, and someone with expertise in social science methodologies.
Then it's a question of who you consult as part of that process. The consultation process and the way that consultation process feeds into the final report is another way in which you can try to balance the views that are heard within the process.