What help do you need with English?
c.1500, from alternative spelling of canvas (n.) and probably meaning, originally, "to toss or sift in a canvas sheet," hence "to shake out, examine carefully" (1520s); "to solicit votes" (1550s). The spelling with a double -s- dates from 16c. Cf. Old French canabasser "to examine carefully," literally "to sift through canvas." Related: Canvassed; canvassing. As a noun related to this, attested from c.1600.