There's usually a coupon for a few dollars off in an upcoming Jean Coutu flyer. I believe the website will mention when it will appear.
And yes, there will be many vendors that will offer Show specials (eg no tax, special deals on merchandise not normally available otherwise). I've been to the BabyTime show in Toronto during the fall, and the Montreal show is 100 times better. Not only because of the vast array of people with products and services to show you. But because it functions as an info fair with government services, non-profit organizations that help parents and families, and groups that work with families touched by a special needs child.
They also provide a drop-in daycare for parents who just want 45 minutes to wander around without a bored toddler to drag around. Boy Scouts are present during the heavy traffic hours to help schlepp the strollers up the stairs for you. And a gigantic sandbox and the eating area includes high chairs for the small fry to sit on. Very thoughtful!