Native Nova Scotian here. I’m so excited for you!!! You will love the east coast :)
Just a couple of thoughts. You mentioned that you want to do Peggys cove and Lunenburg as a day trip. I should point out that these two attractions are both must-sees (see if you can spot the Whales Back rock formation on the side of the road - north bound on route 333!) but these two areas of interest are on opposite sides of St. Margaret’s Bay, over an hour away from each other and each roughly an hour away from Halifax. Add in the fact that if you take the scenic route to Lunenburg (which I recommend), you are looking at single lanes of traffic packed with tourists and, on the Lunenburg side, beach goers, so those times will definitely be inflated. Pro safety tip, for the love of all that is good and holy, read the warning signs at Peggy’s Cove and STAY OFF THE BLACK ROCKS!!!! Even if the water is calm as glass, rogue waves sweep people out every year at Peggy’s Cove and many people have died there. Please supervise any children closely and respect the power of the ocean! A close friend of mine died there a number of years ago - this is not something to take lightly. It is a beautiful place and must be respected.
As others have mentioned, there are so many lovely villages along the south shore, including Lunenburg, Chester, Mahone Bay. The three churches in Mahone Bay is an iconic scene, and is worth the stop. There are also some great shops (support local artists!!) and seafood in the area. When you are travelling between the two, of you make it into the small community of Upper Tantallon, there is a fish and chip shack called “Maya’s Favorite Fish and Chips”, which is next the the Tantallon Esso. Hands down the best fish (haddock) and chips in the area, made by locals (the owners are truly lovely people that live just up the street!) using locally sourced ingredients.
Finally, for PEI. I’m not quite sure why folks are saying not to go there! I live in western Canada now and every summer I go home to NS and I ALWAYS make a trip to the island! The confederation bridge is an attraction all on its own. And the beaches, my dear god, the beaches in PEI are second to none. The water is warm by Atlantic Ocean standards (on the south side of the island). The people are friendly. People are right, there aren’t a lot of “tourist attractions” and droves of tourists flocking to buildings, but the seafood on the island is some of the best. PEI shellfish is the cleanest on the coast (I used to test shellfish for a living, so this is a scientific fact!). Traffic moves slow as you are on island time once you cross the pond :)
Please feel free to message me with any questions! I am proud to say I am a Bluenoser and am happy to help you enjoy your trip. Be prepared - the people there are very friendly :)
Now, you’re going in July, so if you like the beach, consider taking pause and discovering one of Atlantic canada’s phenomenal beaches! If you go further down the south shore you can find some amazing beaches and shorelines to explore. My personal favourite is Hirtles Beach. There is a little day hike you can take; the train head is at the end of the beach and it’s called “Gaff Point.” It’s a little known gem with amazing rock cliffs made is red stone. About halfway through the hike you will find a myriad of Inukshuks that hikers have made out of rocks, making for some really cool photo ops!! Carters Beach is another gem in that area. It is a beautiful white sand beach, but be advised that the water is typically frigid. If you go early enough in the day before the beachcombers have ravaged the shoreline, you might be able to find some sand dollars (please leave the live ones be!). The ovens is also in the area, and while the infrastructure of the park needs some serious help, I can assure you that the views of the caves and rock cliffs is well worth the admission price!