Er, no, it was obvious all along that that was what Trump's team was going to do.  Making our own counterproposals is part of not allowing them to totally control the negotiations.
Moreover, the government's stances are not primarily about backing Mexico.  Trump's demands for the auto sector, for instance, would directly harm Canada's auto manufacture supply chains.  Likewise, Trump wants to eliminate the dispute resolution panels that we depend on to get fair rulings.