The LFS around here used to get them occasionally. But now you cant find any native fish in the stores here. I have caught my share of northerns while fishing and I can tell you they would make one hell of a showcase in your tank. However they get very large. The state record here is 37 lbs 8 oz and 48 " long.
I believe keeping northern pike is illegal in new brunswick (Im assuming your from NB because its the only moncton i've heard of) I would check the laws with your local Conservation officer. I wouldnt suggest you try it either, you would need a tank that is 3 feet wide to house one for more then a couple years.