Here is a link to several in the Halifax area. The closest to the Airport would likely be Dollar Lake, a fairly decent place, but it is back road most of the way from the airport. Laurie Park is close too, a nice park, but we've never stayed there.
FWIW, Amherst is in Nova Scotia and not New Brunswick. Once there, a scenic way to Halifax is via Parrsboro, and there too you will see amazing tides. There are lots of campgrounds from Parrsboro to Truro, one nice on is in Five Islands, where you can walk on the sea floor when the tide is out.
Ed