Under this treaty, if the Canadian government takes actions that damage or undermine Chinese investment in Canada, then Chinese companies can sue Canada in a tribunal that is separate from both Canadian and Chinese court systems; these tribunals have broad authority to mark the findings as confidential, keeping the rulings and outcomes, including financial penalties secret. The duration of the trade agreement is 31 years.
If Trudeau and his Cabinet had endorsed this motion, it would have been a tacit attack on China, and grounds for Canada to be sued under this treaty, with virtually no defense.
Naturally, Erin O'Toole (the current leader of the opposition party in Canada) is aware of this, and the easy political points he can score by attacking Trudeau for failing to support this policy, since he had a direct hand in promoting and passing the legislation.
[1] https://en.wikipedia.org/wiki/Canada-China_Promotion_and_Rec...