The canonicity of the pairing is ambiguous. It was depicted in a single episode ("Chef Goes Nanners"), when
Wendy and Cartman have to work together for a debate. Wendy starts feeling attracted to Cartman, even has a romantic dream about him in one instance, and eventually sees herself forced to kiss him in front of everyone because she wouldn't be able to concentrate otherwise. Cartman is also shown to become nervous in Wendy's presence while they work together, and is visibly happy after she kisses him. However, after the debate, Wendy declares that she doesn't have any feelings for him, leaving Cartman pretty disappointed.
Wendy has the same temperance as Cartman in some situations, which is why some fans support this pairing rather that Stendy.
For instance, Wendy broke up with Stan and went out with Token, and she has had a couple of crushes with other boys during the series. Although Stan and Wendy try to spend time together, sometimes it does not work. For example: the "Eat, Pray and Queef" episode when Wendy wants to study together with Stan, he simply brushes her off. In "Breast Cancer Show Ever" everyone inquires Stan as to what he is going to do about his girlfriend fighting Cartman, but he does not do anything about it, nor does he seem to particularly care. Stan quite often clearly lacks the 'passion', something that Cartman and Wendy both have in their character.
They are both manipulative and they are both good at planning, plotting and achieving what they want.
In addition, they have both killed someone. Cartman was renowned for for killing a couple in "Scott Tenorman Must Die" in which a teenager cheated Cartman out of $16.12. In revenge, Cartman surprises everyone at the end when he reveals that he killed Scott Tenorman's parents in an elaborate scheme. Wendy has also killed someone as well, a substitute teacher when Mr. Garrison was away. She plotted to have Ms. Ellen shot into the sun by using her Arabic language skills to hire agents to do her bidding in "Toms Rhinoplasty".
It is possible that Cartman is lusting after Wendy, rather than actually loving her, and is mistaking his strong sexual desire for her for love. Though, it is more probable that Cartman's constant spiting her is simply a display of 'pulling pigtails'.
Wendy briefly felt attached to Cartman in "Chef Goes Nanners".
In this episode, the kids are forced to do a debate on the changing of the South Park flag. Wendy volunteers to be the team captain for the "Flag Should Change Team" Team whereas Stan is in the opposite team. To her disappointment and shock, Cartman joins her team.
At first, Wendy despise Cartman because of the way he works and his ego, however, Cartman suggests at some point after a couple of meetings that he is willing to help out if necessary. As they do research in the library, Wendy finds out that they have some points in common, like quadruple stack oreos they both enjoy. Later in her dreams, Wendy fantasizes that she wants to be together with Cartman.
Scared because she is still in a relationship with Stan and knowing about Cartman's egoistical nature, she seeks Bebe's advice. Her friends assumes that it is because of 'sexual tension' after working together for such a long period of time.
This deeply affects her concentration during the debate, unable to continue, she rushes to Cartman and kisses him in front of the South Park citizens, including Stan. Obviously shocked but ecstatic, Cartman taunts Stan across the room while Wendy and Kyle continues their debate.
After the debate, Wendy is seen with Cartman as she informs him that all the feelings that she had for him had dissolved much to Cartman's disappointment.
The idea hasn't been revisited since then.
This pairing, from Wendy's side, may have been hurt by the events of "Breast Cancer Show Ever". Although it could be argued Cartman didn't want to fight her as he did love her and not due to intimidation as the episode strongly implies, Wendy beats up Cartman with little hesitation outside of when her parents forbid her to.
However, it seems that there is new evidence that he might still want Wendy's attention in the episode of"Fishsticks" when Cartman subconsciously remembers things incorrectly due to his ego. In his one flashback, after he slays a dragon and saves the city, Wendy approaches saying: "And He's not fat at all." and then during a second flashbacks, "You saved everyone from the "Jewbots Cartman!"
In "Mr. Hankey, The Christmas Poo" Wendy (Like everyone else, except for Kyle) clapping at Cartman's classic song "Kyle's mom is a bitch".
In an interview with Trey & Matt on their official website, there was a question that was about Cartman's love interest: All the other boys have hooked up with chicks before. Will Cartman ever get a love interest besides money?Trey: Cartman is too selfish, and I remember that he did have a thing with Wendy the Flag epsiode I think. Matt: Yeah, they kiss.
On the official South Park Studios Website FaQ:
Sunday, February 1, 2009I cannot find the episode when Wendy and Cartman kiss. Wanna help me out?Sure. It's from "Chef Goes Nanners" in Season 4. People forget that Wendy and Cartman had this little make-out sesh, especially after Wendy kicked Cartman's ass this season. But boy, did it happen.