With six people, I suggest that you reserve a taxi service in advance. According to http://www.tourismsaintjohn.com/
, there are taxis available at the pier, and they charge a flat rate of $50 (US/Canadian) per hour for up to four people, negotiable for longer distances. (Search for "taxi" to find this information.) The site also has links to various taxi/tour companies. I haven't done this -- we've always navigated Saint John by foot or by ship tour, so I can't make a recommendation, but at least it's a start.