I have a hard, painless lump on the roof of my mouth. i noticed it yesterday because it hurt to eat. could this be oral cancer?

Hard to say...: Diagnosis for lesions need every bit of information... how long has it been there? How big? is it getting bigger? Condition of your adjacent teeth? Location on the roof of your mouth? Social habits including drinking and/or smoking? See a local oral surgeon for an exam.

Tori.: Likely Tori. See: https://en.wikipedia.org/wiki/Torus_palatinus But: See oral surgeon or ENT doc if you have any of these symptoms: Persistent mouth sore, persistent mouth pain, a lump or thickening in the cheek, a white/red patch on the gums, tongue, tonsil, or lining of the mouth, a sore throat, hoarseness or feeling that something is caught in the throat that does not go away, difficulty swall

Lump: Probably a Torus Palatines, a harmless boney outgrowth. Appears in about 1 out of every 4 people. That said, any bleeding, or as in your case swelling or pain (can't be both "painless" and "it hurt to eat") should be immediately investigated. Please see your Dentist or an Oral Surgeon for evaluation.