>>149764790
According to FusionFall, Marie likes Edd because he is smart like her.
>"Marie Kanker: The middle Kanker sister, Marie is neither as nasty as Lee, nor as absent minded as May. If anything, Marie is the brains of the outfit, and as such, she has a thing for Double-D."
https://web.archive.org/web/20100820214552/http://fusionfall.cartoonnetwork.com/game/about-characters.php