Buy the Allstays app, its what we use on a Ipad. Its also for androids to.

We use a few different apps and websites. Freecampsites.net has proven to be our most useful.

I think you will find that Nova Scotia will have limited boondocking opportunities. Like the US east coast, it was settled a long time ago and much of the land is in private hands. Not much public land was preserved like out west. And the Maritime provinces are on the small side.
Here is another camping app that lists public campsites - http://www.ultimatecampgrounds.com/index.php/products/full-map Most will be Provincial or National parks.

Maybe clubs like Boondockers Welcome or Harvest Hosts could be of use.

www.campendium.com is another option for free or low rate.

Like Ray said boon docking is not common at all in NS. I would suggest provincial parks or federal park and both are accessible for online bookings. My favourite provincial parks are Rissers Beach and Graves Island both of which are located in scenic and historic spots. If going to Cape Breton I would suggest the provincial park at St. Peters as I would not tow to the federal park due to the steepness of the highway or travelling as far as Port Hood or Cheticamp and travel the Cabot Highway just in your vehicle. It's a spectacular drive. Fees at these park are all reasonable.

Make sure you go check out Oak Island.

This is a shot of my allstays app off Ipad.

Canadian Tire in CAN allows for overnight parking, like Walmart
we stayed in Fundy Natl Park for a few days prior to traveling TO NS.. nice park, GREAT hikes in Fundy
we stayed in Scotia Pine CG near truro (meh)
we stayed in King Neptunes CG near Peggys Cove, OK CG, but amazing sunsets. nice hikes and kayaking nearby, plus stuff to do.
we stayed in Bras'dor CG, nice CG, used it for take off point for many things on the norther part of the island
we stayed in Digby CG, again meh, but used for take off point for things to do around the area.
we dont spend much time in the Campgrounds. we mainly use them to park the RV to sleep, and spend the whole day exploring the area around it. there is LOTS to do/see in NS, but dang its a BIG island. Point a to point b looks easy on the map, but can be real far apart 100 miles+. we spent many a day just traveling to and from. We tried to find a CG/or park centralized to an area... stayed for a few days to explore, then move to the next area. We did enjoy our 2 weeks very very much in NS, and i'm sure you will too.

if you are military or a vet there is a couple bases that have campgrounds. Biggest tip I can give is .. Don't rush. We spent 8 days in NS last year and that wasn't long enough.

Hi, Fortress Louisbourg on Cape Breton is well worth the visit. The University students re-enact life there … including at the entrance, where they make sure you're not a British spy!! Saying "Vive le Roi" works.

Here is an old video I found from our visit to Fort Louisbourg in 2011
Sorry about the poor quality, only had a little point and shoot camera way back them. Was a fun place to visit.