Despite what some claim, there is really nothing that secret about the Security and Prosperity Partnership. Both the U.S. and Canadian governments have had informative websites on the initiative for some time. Mexico probably does too (although I'm not inclined to search for it). There is more than enough to debate and discuss without making stuff up.
For the most part, it is hard to argue against a cooperative approach to trade and security issues. In the end, if Canadians don't like what the Harper government agrees to, they will eventually have recourse at the polls. There is nothing anti-democratic about that.
Of course, Harper will have to be on guard against U.S. efforts to load the SPP with extraneous commitments. Michael Geist points out how the U.S. managed to slip in its intellectual property priorities in the final agreement. I'm not too keen on Harper giving in on that. Still, the SPP provides an indispensable forum to address common issues and, ultimately, to protect our economic interests. It would be foolish not to participate.
Update: New source of video provided as previous source expired.