There are many characters in Cars, many of which are playable in Arcade mode. But to unlock a character, you need to buy them from the Bonus Features shop with your points.
Playable
Lightning McQueen
A race car whose number is 95 after the year where Pixar release their first featured film, Toy Story. He is a race car sponsored by Rust-eze. He doesn't have any friends except for Mack when he was a racing car. He's the main playable character is most races.
Mater
A old and rusty tow-truck, he's been living in the junkyard for a while in Radiator Springs. After an incident when Lightning McQueen entered Radiator Springs and was messed up. Mater became best friends with Lightning McQueen because Mater knows that Lightning was a famous race car. He also appears in the Tractor Tipping mini game.
Sally
A blue car that lives in Radiator Springs. She first appears when Lightning McQueen is at court with Doc Hudson. Then later, Lightning McQueen becomes friends with Sally because Lightning McQueen thinks she is pretty cute and Sally takes Lightning McQueen on a ride to Tailfin Pass. She is a friend of Lightning McQueen and also she appears on the race where McQueen and Sally have to race through Tailfin Pass.
Doc
Doc Hudson is a big blue car and he is also known as famous for being as Fabulous Hudson Hornet when he won three piston cup races. His Hudson Hornet career ended when he got into a terrible crash when at the final lap of the 1954 race. He first appears at court, where he acts as a judge for Radiator Springs, where Lightning McQueen was accused. Also, he talks about Fabulous Hudson Hornet when Lightning McQueen goes into Doc's doctor house.
Sherrif
A big police car and the only police car in Radiator Springs. He always sleeps next to the "Welcome to Radiator Springs!" sign. He has to sleep next to it just in case of speeding cars entering Radiator Springs. The sign appears in the valley near Radiator Springs. He's very fast but it's easy to beat him for shortcuts at the race where you don't want the police car to win. He always look for speeders around the town of forgotten Radiator Springs.
Ramone
A purple wide car, he is friendly to Lightning McQueen after the race car messed up Radiator Springs by accident. He has fire decals on his side. You can play him on arcade races if you like.
Flo
A green style car most known for owning Flo's V8 Cafe, which serves oil to cars that are hungry and thirsty. Flo is another friend of Lightning McQueen. Flo's V8 Cafe can be located next to the gas station at the 4-way intersection.