canvasser vs petitioner

canvasser and petitioner both are nouns.

Word	Noun	Adjective	Verb	Adverb
canvasser	Yes	No	No	No
petitioner	Yes	No	No	No

As nouns, petitioner is a hypernym of canvasser; that is, petitioner is a word with a broader meaning than canvasser:

Other hypernyms of canvasser include requester, suppliant, supplicant.

canvasser (noun)	petitioner (noun)
someone who conducts surveys of public opinion	one praying humbly for something
someone who examines votes at an election	someone who petitions a court for redress of a grievance or recovery of a right
a petitioner who solicits contributions or trade or votes
a person who takes or counts votes