Vancouver to Los Angeles, what are the places to stop and see?

I've done that drive.  This is what I did on the way:  

1.  Stop in Seattle.  Space Needle, Pike Place Market, possible a baseball game at Safeco Field.  Continue south on Interstate 5 to Portland where there are lots of microbreweries such as Deschutes Brewery Portland Public House.  After you get through Grants Pass head to the coast to Hwy 101 and then Hwy 1 (Pacific Coast Highway).  You can pass through famous California Coastal towns like Mendocino, Jenner (California) and Bodega (where the Alfred Hitchcock movie "the birds" was filmed) before you get to San Francisco (crossing the Golden Gate Bridgeand then you can check out places like Fisherman's Wharf & San Francisco Chinatown.  After that you can pass through San Jose to get to Monterey where they have the Monterey Bay Aquarium.  Continue south on Hwy 1 to Carmel,  a quaint town that Clint Eastwood was once Mayor of.  Stay on hwy 1 and you'll drive the cliffs of Big Sur

Once you get to San Simeon Lodge, stop in to see the Hearst Castle

Right on the coast in the Hearst Castle area you'll see beaches with hundreds of elephant seals on them.  It's quite a sight.  Once you get to San Luis Obispo, go north on Hwy 101 to Hwy 58 and take that east through Bakersfield (home of the "happy cows" - lots of huge farms there) and on to Barstow.  In Barstow, get on Interstate 15 North towards Las Vegas.  On the way, you can go to Death Valley National Park and see the Worlds tallest thermometer!.  Of course in Vegas, there is a complete list of things to see and do on the Las Vegas Strip.

To get to Los Angeles, just return back down on Interstate 15 south...

That's quite the epic trip Mark! So I'm going to start with where I think you can skip. I think a lot of the tip-top of Northern California you can skip. I don't think the Nor Cal coastline really gets awesome until Fort Bragg in Mendocino County, where the coastline gets really dramatic. Stop at Glass Beach, which is really interesting and if you love beer, North Coast Brewing Company, which is one of my favorites. Continue down the coast past Point Arena and Point Arena Lighthouse and Museum and Sonoma County, which is a lot of people think for its wineries, but has great offbeat beaches as well. Sonoma County is my favorite California wine region, especially Healdsburg.

From there, onto San Francisco. Between SF and L.A., the best coastal portion is between Santa Cruz and Morro Bay. I wrote a guide about traveling through that section here: 

http://whiskeytangoglobetrot.com/guide-pacific-coast-highway-big-sur/

Highlights: 

Nepenthe for the views.

Pfeiffer State Beach for an offbeat beach.

McWay Falls

Hearst Castle Rd

The other part of that drive I know well is the Oregon coastline. I think it really gets overlooked by the California coastline, but is equally beautiful. I wrote a guide here on Yahoo:

https://www.yahoo.com/travel/highway-101-up-the-oregon-coastline-107518475517.html

Highlights:

Oregon Dunes National Recreation Area

Sea Lion Caves

Tillamook Cheese Factory

Cannon Beach

Astoria

So many cool places to stay. If you like city life stay somewhere in Downtown Los Angeles like The Standard Downtown LA or the Millennium Biltmore Hotel. The Millennium is old school elegance. Since your in downtown you are close to everything. Hit up the Getty Museum, Griffith Observatory and Sunset Blvd. Hollywood is sooo touristy (if thats a word). If you go to a beach hit up Venice Beach, Santa Monica and Hermosa Beach. Word of caution. This is LA and traffic is bad. But if you leave in the morning you will hit a lot of the beach going traffic. The later you leave in the day the worst it gets on the weekends. But weekdays 11amish is is good to go. If you are not renting a car use Lyft or sidecar. Super cheap. Here is a promo code for ride credits for you to use on Lyft RAUL093752. Have a blast.

I cannot answer for the entire trip, but my family and I have been back from our trip to Oregon for about three weeks. Some of the places I'd like to see again:

Oswald West State Park

Haystack Rock at Cannon Beach

Vista House in the Columbia River Gorge along with Multnomah Falls.

People have already left some great suggestions, so I'll just insert a few additions:

In Seattle, you might try:

• Seattle Aquarium  It is on the water down from Pike St  Fantastic.

• Ivar's Acres of Clams for clam chowder and more.
  
• Attend a Seattle Sounders soccer game.  The crowd is the best in all of MLS.  It is generally sold out and 60K.
  

Columbia River:

• See the massive sturgeon at Bonneville Fish Hatchery and see the salmon ladders.
  

Oregon

Downtown Portland, brewery crawl.  Park in downtown, start walking from brewery to brewery.  Here is a Google map link and graphic map of them:

https://www.google.com/maps/search/best+breweries+in+Portland/@45.5207912,-122.6726182,13z

Crater Lake National Park

If you golf, Bandon Dunes Golf Resort

California

Point Reyes National Seashore

Monterey Bay Aquarium

17 Mile Dr

Ventana Inn & Spa

Piedras Blancas Elephant Seals

Hollywood Bowl  See a performance at the Hollywood Bowl.  Pack a picnic basket and wine, arrive early.

Laguna Beach

Petco Park  Take in a Padres game.

and that's it for me.

Hi Mark. there are a lot of things you can do around LA in 20 days. I would recommend you to visit San Francisco rent a car and drive all the way up through Pacific High way. You will enjoy amazing views, farms, cliffs, beaches, Monterey, etc. It is just spectacular! Then you can come back to LA and head to Las Vegas, which is a party city, but you can also go to Grand Canyon National Park and Hoover Dam. Enjoy your stay :)

Wow, fantastic trip! I'll second the Hearst Castle suggestion and add that the night tour is really fun. The van drives up the hill and the whole place is lit up. Docents dressed in period costumes discuss events of the day.

If you make it down to Laguna Beach and it's during the Sawdust Festival, you could spend the day wandering the festival and hanging at the beach and then at night check out Pageant of the Masters. Locals dress in costumes and pose to recreate famous works of art. It's totally unique, charming, outdoors and slightly cheesey in a great way.