Ford will unveil the 2013 Fusion Cup car on Tuesday.
NASCAR's essentially doing the same thing they did in Nationwide: rather than mandate the same body, they are mandating the same drag and downforce numbers. It worked well in NNS; all four manufacturers, even with their varying levels of representation, went to victory lane in 2011. Solves the problem of everyone complaining that someone has an advantage, while also solving the problem of automakers complaining that they have no brand identity in NASCAR.
The chassis will not change, so don't expect a real difference in the style of racing. Still a welcome change, in my opinion, and the only way to really go about it as, if you free them up, they'll just design super aerodynamic cars that look nothing like production cars as opposed to the super un-aerodynamic cars that look nothing like production cars we have now.
Dodge will use the Charger in Cup. Toyota will use the Camry. There is a new Impala for 2013 so one assumes Chevrolet will use that; they could use the restyled 2013 (or 2012?) Malibu as well, or even the Caprice (basically a Pontiac G8/Holden Commodore) that is currently a police car but eventually supposed to maybe possibly sort of go on sale as a production car if I'm reading things correctly.