I did manage to time most of our journey on the way back. Here are rough timings:

Halifax-border with New Brunswick - 2 hours
across New Brunswick - 4-5 hours
New Brunswick northern border to Riviere du Loop - 1 hour
Riviere du Loop to Quebec City downtown - 2.5 hours

That makes the total time about 10 hours on the motorway/freeway. Of course, stopping and getting on smaller roads meant it actually took longer.