To sift; to strain; to examine thoroughly; to scrutinize; as, to canvass the votes cast at an election; to canvass a district with reference to its probable vote.(verb)
source: webster1913
To search thoroughly; to engage in solicitation by traversing a district; as, to canvass for subscriptions or for votes; to canvass for a book, a publisher, or in behalf of a charity; -- commonly followed by for.(verb)