Nintendo Power said that Delfino Hills from Mario Kart DS would be a retro course. However, it is already a retro course in Mario Kart Wii, so therefor, the idea had to be cut.
In the game's files, there is a file called "05gingerbred.ex". When opened, the course is confirmed to be called "Gingerbread Lane", and it looked like the walls and tunnels and bridges of the course were made out of gingerbread. It's possible that Gingerbread Lane was replaced by North Pole Pathway.
Also in the games files are models for Baby Wario, Shy Guy, Hammer Bro., Magikoopa, and Shadow Mario. Baby Wario and Shadow Mario were most likely replaced by Baby DK and Metal Mario, the others were cut for unknown reasons.
It was shown that the Thunder Cloud from Mario Kart Wii and the Tanooki Leaf from Mario Kart 7 were supposed to return, but were cut for unknown reasons.
In the demo, there was an item that resembled to watch from Super Smash Bros. Brawl. It stopped other racers for a short time. It was cut for two reasons: It gave the player or CPUs an unfair advantage, and people who were victims of this watch thought the demo froze mid-game.