The Grand Canyon is beautiful, if you have time to make a detour the Sky Walk is pretty cool, it's a glass bridge over the canyon that you can walk on. It's on the west end of the canyon on the Hualapai reservation though, outside of the national park, it's a bit of a drive and a little pricey, less crowded though. I personally preferred to stay in the national park because I thought it was prettier with more to do (hiking, biking, or just driving the scenic route around the canyon) and I wasn't too thrilled with the bridge, but I don't know anyone else who's done it and shared my opinion on that, they've all loved it.

There are lots of hiking trails all over Big Bear with pretty views of the mountains, unfortunately the only one I've taken is South Fork Trail and I didn't make it far so I don't have much to report on that. There are also a lot of places to rent bikes for the trails, and canoes or kayaks to take out on the lake. I also noticed while I was up there this weekend that they now offer zip lining...I didn't try that while I was there but both of the places that offer it have 4 stars on yelp!

Once you get to Laguna Beach, Crystal Cove is a great place to hike. You'll get a nice view of both the hills and the beach, you only have to cross the street to get to the beach afterward too. Laguna Beach will also be having the annual Sawdust Art Festival when you arrive (June-August) if you're interested in checking out local art.

Your whole trip sounds like so much fun, I hope you have a great time! Feel free to pm me if you have any questions or need any help while you're in California :)