Just wanted to make sure that when you research via external websites, you look for things pertaining to Saint John, New Brunswick.
St. John (or St John's) is Newfoundland - different province, although still the Maritimes. It was one of those annoying little hick-ups in Canadian Geography/History class.
I'm Canadian and I still haven't been to New Brunswick - but I checked out the excursions and I'd probably do the MooseHead excursion just because it's got that east coast pub/entertainment vibe is I wanted a taste of the local vibe in 3 hours.
The real gem is the Bay of Fundy (as you can probably tell by all of the excursions that have Bay of Fundy thrown in) - it's probably considered a must see if you were to go on vacation there - they have the highest tide in the world I believe. It's also probably pretty beautiful.