A chancre doesn't cure syphilis. A chancre is the characteristic skin lesion of early syphilis.

No, chancre and canker are not interchangable. A canker sore is a benign and painful sore on the mucous membranes. A chancre is a painless ulcer on the mucous membranes that is a specific sign of syphilis.

Primary.
The first stage of syphilis is where a chancre appears at the site of infection.

A patient presenting with a chancre can get tested with serum testing for syphilis. More rarely, the health care provider may examine exudate from the base of the chancre with dark-field micropscopy to check for the spirochete.

You can put iodine on the chancre sore. But please do not forget to visit the physician. That is must for cure of the disease.