In New Brunswick: Hopewell Rocks to see the 40 foot tides and walk on the ocean floor. You can see both tides in a 6 hour period, check online for tide times.
In Halifax:
We have stayed at Woodhaven RV park, nice owners and convenient, although not on the water.
You may like to check out Shubie Park (busy on weekends but has bike paths etc.) or one of the parks on the coast - we stayed at Murphys on the Water a few years back and it was great. The KOA in Mt. Uniacke is not far from the city either.
Be sure to spend time on the waterfront in Halifax - the busker festival is on from August 5th - 15th. Also Pier 21, the Citadel, the Museum of the Atlantic....
Is Halifax your destination, or will you be going other places in the province? How much time do you have? A trip to Nova Scotia isn't complete without seeing Cape Breton (leave your trailer in Wycocomagh and drive around the Cabot Trail), and you can go home via Prince Edward Island. Take the ferry from Nova Scotia, drive down the island and then cross to New Brunswick - a few dollars cheaper as you only pay to get off the island, and the bridge is marginally cheaper than the ferry.
There is the whole rest of the province too - from Halifax to Yarmouth either along the south shore or through the valley, all lovely country.
Check it all out online before you come - you'll end up with more ideas than you will have time for
Our home is Nova Scotia, so feel free to ask us any questions! Also, each province has a tourist guide that you can have them mail to you. Mail from Canada to US takes extra time, so you'll need to do that right away.
A note about crossing the border: check online to see what you can and can't
bring across. No guns! The crossing at St. Stephen/Calais is more scenic, but we've found less hassle at Houlton, but that's just our experience. We used to have a bigger rig, and I think the border guys just wanted to check it out. Houlton is a larger crossing and they are more used to big rigs there. Our present rig shouldn't be a problem anywhere
Happy travels!!