Can you tell me how to know the difference between a canker sore and oral cancer?

Pain: A canker sore is usually painful but likely will resolve in 10-15 days. Oral cancer is usually not painful until later stages. It can have many different appearances so it's not easy to diagnose visually. It will not resolve in 2 weeks. See a dentist, oral surgeon, or periodontist if the lesion is present for more than 2 weeks regardless of how it feels.

See any dentist: for cancer screening examination and differential diagnosis. The only way to definitively determine whether you have oral cancer is to remove some abnormal cells and test them, hence most dentists use OralCDx Brush Biopsy for this task.