The main reason I went to Fredericton is primarily to go shopping. The Regent Mall has a great selection of shops. Even though the stores themselves are the same as where I am located an hour away, the variety and size is more so it makes for more productive shopping. There is a Chapters Bookstore as well which is great, I could spend days in there.
For sightseeing, I haven't done a whole lot. I know from previous trips that Woolastook Park is great for the kids, with a zoo and waterslides. For older folks, there are lots of beautiful parks and a walking trail along the river is always nice (when it's not flooded in the spring!!). The nightlife is great in Fredericton and dining options are a plenty. Definitely a great spot for a long weekend away!!