Personally I'm concerned about allegations that it could allow corporations to sue the Government of Canada (read: taxpayers) for any laws that harm their profits. I worry it means that corporations will exert tremendous influence on what laws do and don't pass by way of threatening to sue, and they can effectively tax us by way of lawsuit settlements if the government doesn't comply.
Either way, it seems like a shifting of power from nation states where we (debatably) have a say in how things are run to corporations where only major shareholders have influence. A shift away from the nation state model of governance and towards a feudal corporatocracy.
This is an excellent question, and something that I think is going to be unanswerable. The fact is that NAFTA has been in full effect for decades and on all sides there are breeches. These breeches come in front of the WTO from time to time (most recently I remember country of origin labeling). Mostly I am interested in more informed answer and am bumping (is that the term here? I am new) for visibility and hopes of a real answer/debate.