petitioner vs canvasser

petitioner and canvasser both are nouns.

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

As nouns, canvasser is a hyponym of petitioner; that is, canvasser is a word with a more specific, narrower meaning than petitioner:

Other hyponyms of petitioner include besieger, postulant, solicitor.

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