Is a canker sore a form of herpes?

No, not herpes: Cold sores (see picture) are on the lips or on the face. They are caused by recurrences of herpes virus, which lives in the nerves after an initial infection, and then travel down the nerves to cause the cold sores at the skin surface from time to time. Canker sores are inside the mouth, and are not from herpes, but are due to the immune system reacting to something on the inside of the mouth.

No: A canker sore is an aphthous ulcer. It occurs indifferent locations than herpetic ulcers. Herpetic ulcers are caused by a virus and occur on the vermillion border of the lip. Aphthous ulcers are on the cheeks and tongue and caused by trauma, stress , hormonal, etc.