If the sand beaches are the prioity the beaches along the Northunberland strait are your best bet, but farther removed from the biggest points of interest. There are some nice beaches along the southwest shore, but weather can play the devil there. The plus is your proximity to some of the most beautiful and interesting places in the province. Best way to enjoy the province is to pick 2 home bases for you adventure and go discovering from there. Roselawn cottages in the town of Wolfeville is a nice spot to tour the Fundy shore from. There are a few cottages and motels just outside Lunenberg, name escapes me after some 10 years back, on the shore that were nice.
By the way, smallmouth fish is a blast on the inland lakes.