To add to what was already mentioned above:
California Adventure
In Pixar Pier area you can also meet Woody, Jesse, Mike Wozowski, Sadness, Joy, many of the Incredibles and I am sure there are more.
I think you can also meet Raya at the challenge trails. You used to see brother bear characters, but I don't think they have been out for a while.
Lightning McQueen and Mater at Carsland
Anna and Elsa usually in the area where Animation Academy is located (inside)
On Buena Vista street you will usually see the fab five along with Oswald (near the entrance) and sometimes some others like Clarabelle, Chipmunks, and Max Goof.
Disneyland:
At the entrance as you walk in, there are often characters, usually a princess.
At main street area its the fab five and chipmunks usually and sometimes some other characters might show up.
New Orleans Square and Critter Country - Tiana and Dr. Facilier in New Orleans and sometimes Jack Sparrow in Critter Country you get Pooh, Tigger and Eyore.
Black Spire (Star Wars) - R2D2, Rey, Chewbacca, Baby Yoda (Grogu), Kylo Ren, Storm Troopers
At the Royal Hall there are princesses. They rotate in and out so you never know who is there.
By Big Thunder and the Rancho Del Zocalo you will sometimes see Miguel but he may be seasonal
Walking around the center area and the castle area sometimes you will Mary Poppins and Bert, Alice and the Mad Hatter, and other characters.
In Toon Town - Fab five - but this is undergoing renovations so by the time you go it may change a bit. I would still expect to see the fab five.
Check out the Tomorrowland Theater they will sometimes have a variety of characters there unannounced.
Walkway from teacups to Small World you will sometimes find various characters. Often I see Merida here.
My daughter is a CM and I will ask her if there are any others that I am missing.