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.