On the one hand, I think that the Liberals only promised to get out of the air mission to pander to the perceived pacifists who supported the NDP. In the past, the Liberal Party supported Canadian participation in Canadian bombing campaigns (Kosovo). The training but not combat line never made a heap of sense other than as a campaign strategy.
On the other hand, I prefer not to overreact to terrorist attacks since that is what terrorists want--to get you to do what you would otherwise not to do. So, switching from the planned policy because of Paris would seem to be wrong.
So, stick with a flawed policy resolutely or adapt to new circumstances, getting out of a lousy stance, but appear to be reacting to terrorism.
Of course, the larger questions are what should matter most: is the bombing working? Is Canada's participation meaningful? Is it easily replaceable? Oh, and how to pay for it (because that matters, too)? Regarding the last, one of the problems Canada has is that its operations come out of the regular military budget, squeezing other stuff. So, yes, opportunity costs exist.
Oh, there is a moral challenge here--if Canada's pilots have more restrictive rules of engagement, letting others do the bombing in our stead might mean more collateral damage. And, yes, I am pretty sure that France's rules of engagement are less restrictive right now than pretty much anyone in the coalition effort.
So, where does that leave us? I think Trudeau can play it either way. And the folks who study Canadian IR predict he can go in either direction. Which way will he play it? I would bet on Trudeau staying the course, but my bet would be small. Which way should he play it? Perhaps commit to continue the mission until the year is up from when parliament last voted (last winter) and then see where things stand? Again, the effectiveness/efficacy should matter somewhere in all of this, so I will use that as my dodge.