Cars was one of Pixar's first animated movies. The story followed Lightning McQueen (voiced by Owen Wilson), along with several other talking cars, as he tried to achieve his dream of racecar driving. The movie has had two sequels so far that have also focused on McQueen and best friend Mater (Larry the Cable Guy), so Cars 4 will most likely focus on these two characters again.
Although Cars 4 isn't for certain and Pixar could be working on various other projects before a new movie in the franchise, there are some actors who should definitely return if Cars 4 does happen.
Tony Shaloub - Luigi
Tony Shaloub has voiced Lightning McQueen's friend and part of his lightning-fast pit crew, Luigi, for the three movies in the franchise. Luigi has been faithful and followed and supported McQueen in all of his races, so it would be odd if Luigi didn't return for another installment in the franchise.
Cheech Marin - Ramone
Cheech Marin has voiced Ramone in the first three movies of the franchise and should return if a fourth installment is made. Ramone helped McQueen with repairs and looking professional after his racecar training was done.
Ramone, similar to Luigi and most of the Route 66 friends from the first movie, has supported McQueen since the beginning and should be brought back for Cars 4.
Jenifer Lewis - Flo
Jenifer Lews is known for her role on Black-ish, but she also voiced Flo in all three movies of the Cars franchise. Flo and Ramone have been together for the three movies and both chose to become close to McQueen and help the aspiring racecar driver achieve his dreams. Flo is just as capable of adding style and flair as Ramone is and the character should be brought back if a new movie is made.
Michael Keaton - Chick Hicks
Michael Keaton only had a small role in the first movie, as one of McQueen's fellow racecar competitors once Lightning started competing in the bigger races. Hicks was found out to be a cheater and McQueen won the races against him fairly.
Apparently, Hicks' entire career was ruined after everything was revealed, so it would be interesting to see them revisit a storyline with McQueen's first enemy.
Richard Kind - Van
Richard Kind voiced a van in the first Cars movie and made a cameo in the second movie, as well. Kind's character was trying to travel on a long journey with his wife, but the two always seemed to be going the wrong way or running into some issue on their trip.
It was a recurring joke throughout the first movie and it would be fun to bring back Richard Kind's recognizable voice as the character who always seems lost.
Bonnie Hunt - Sally Carrera
Bonnie Hunt voiced Sally, Lightning McQueen's love interest and a major part of his support system as he first began training to be a racer.
The character has appeared in the three movies and should be brought back for a fourth, especially if it again centers on Lightning McQueen since the two are so close. Sally stayed a main character in the franchise so far and will probably return for Cars 4, if it ever happens.
John Ratzenberger - Mack
John Ratzenberger has voiced countless characters in Pixar animated films, and the Cars franchise is no different. He most notably voices Mack, who is a good friend and supportive of Lightning McQueen.
He's the one that helps McQueen get to all of his races and makes jokes along the way. Ratzenberger has voiced Mack in the first three movies and would likely return if a fourth installment in the franchise does happen.
Michael Caine - Finn McMissile
Michael Caine is a distinguished actor who lent his voice to Finn McMissile in the second Cars movie. McMissile is a British spy car who mistakes Mater for an American spy car and recruits the rusty pick-up truck to help save the World Grand Prix.
Although Caine only voiced this one character in Cars 2, it was such a different storyline from the first movie that it would be interesting to return back to the spy world, or at least check up on what the British spy car is up to.
Eddie Izzard - Sir Miles Axlerod
Eddie Izzard voiced the main antagonist in the second Cars movie and is primarily who the spies are looking for to save the World Grand Prix. Axelrod wants to sabotage the race to protest alternative fuel, but the villain is thwarted by the heroes.
Izzard is a recognizable comedian and Cars 4 checking in on past villains could be an interesting plot for a new movie.
John Turturro - Francesco Bernoulli
John Turturro voiced Francesco Bernoulli in the second Cars film and is another antagonist to Lightning McQueen's protagonist. Although he only appears in the second movie, Bernoulli is a former rival of McQueen's and has an interesting Italian racecar design that makes the character more fun, matched with Turturro's voice acting talents.