In order to best answer your question, you need to be more detailed about what the lies are. Did it have 100 or 10,000 miles instead of 10? Was it a demo sold as new? If yes, you likely would have a fraud claim against the dealership. You likely can't "cancel" the contract, but could force the dealership to buy the car back from you for what you paid for it. If there definately is fraud, you should contact an attorney in your state as there is likely a consumer protection law that will give you attorneys fees to go after the dealership. Don't go it alone.
In most states you probably have the legal right to cancel it as long as the vehicle you bought is still in substantially the same condition as it was when you bought it and the "lie" by the dealer is "big enough" or important enough to the deal you made. If the vehicle isn't, then you can still claim damages that resulted from the lies in order to get back some of your money. If the dealer set up your financing, and it sounds like he did, then it can be a violation of the Truth In Lending Act to represent that you have to buy a service contract as part of the deal. There's also a federal odometer law and usually every state has its own odometer law that governs exactly how the mileage is supposed to be disclosed and what happens if a car dealer does it wrong. To know your legal rights for certain, you need to find an attorney in your state who handles "autofraud" cases. But don't wait very long because for every legal right you have, you also only have a limited amount of time to do something about it or your rights are lost forever.