We normally have two dogs and travel all over around here. We just got back yesterday from Whidbey and our pup was with us. As mentioned, Ebey's Landing is a great easy hike with a dog and Double Bluff Beach, Meerkirk Gardens, Deception Pass State Park, etc. I can't think of anywhere on Whidbey that is not dog friendly.
We don't normally take her over to the Olympic Peninsula because the park does not allow dogs, so it gets pretty limited. There are some nice rustic cabins at Kalaloch that we have stayed at with our previous dog, and that was nice. The cabins have mini kitchens in them, which is good because there isn't good food to be found nearby.
The Leavenworth area is great too, and another area we take our dogs. We like to rent cabins in this area and usually go through NW Comfy Cabins. There is the downtown area of Leavenworth (very dog friendly) and then Blackbird Island which is a great place right in town along the river to let your dog swim or just cool off. Plus so much in the general area.
Sunriver down in Bend is fabulous in July with dogs. It can get hot, but it is a dry heat. I am a heat wimp and am fine there, FWIW. There are so many home rentals that we usually go there for a solid week, and we have been doing that for many years.
Also the OR coast. Cannon Beach or Manzanita are both extremely dog friendly. Finding a place for July might be tough at this point, but worth a look! Our favorite place to stay in CB is The Surfsand Resort, which is extremely dog friendly, and has been our go to place for many years. I used to go there as a kid even.
On the southern WA coast, Westport Marina Cottages are dog friendly and we have taken our dogs there a handful of times. I love that the cottages are walkable to a couple different beach areas, and it is a short drive to Grayland which is a wonderful wide open beach. Good restaurants are lacking here, but there are a few fish n chip type of places.