Beach Area 3
There are two features which make Beach Area 3 stand out: a) The Provincial Park office is located there, and b) this is the only beach where you are allowed to bring your dog.
The beach is heavily patrolled by the Ministry of Natural Resources staff and they are dead serious about keeping dogs away from the other beach areas. This attitude isn't to be unfriendly, rather it's in-part a measure to protect sensitive wildlife and to comply with the regulations of a Blue Flag Beach. But trust me, this is a good compromise because Beach 3 is central, has fantastic sand quality and it's wonderful to watch the dogs romp and play with the sheer joy of being alive. If you don't plan to bring your pet to the beach but you still want to give him a run before you enjoy the sun and sand, you can always bring fido to the dog park located beside the RecPlex at 1724 Mosley St.
I happen to think that Beach Area 3 is one of the nicest spots in all of Wasaga Beach. If you were to look at Wasaga on Google Maps, you'll see that the shore curves quite significantly between Collingwood and Allenwood Beach. There is no better view of the entire shore and the Blue Mountains as can be had at Beach 3. You will also see the lights of Beach 1 at night. The water looks deep blue or teal here and can provide some stunning photographic opportunities.
The image below shows where the amenities are located for Beach 3.