The concern is, what if Canada doesn't ratify the agreement, though? And that is directly related to the costs of not ratifying. We've seen what happened with the Korean deal, and we certainly cannot relive that experience again. Who knows what would happen if Canada were not part of the TPP? That's the first part of the answer.
The second is, if Canada is not part of the TPP and other signatories are, our products would not qualify as TPP-originating, so we would not have access to that huge trading bloc that is growing ahead of us.
To your question of what is the concern for Canada, I would say that it's more about looking at the risks and the costs of not ratifying the TPP at this point.