c. 1500, "toss in a canvas sheet," from alternative spelling of canvas (n.). From "toss in a canvas sheet for the purpose of sifting" the meaning was extended figuratively to "shake out, examine carefully" (1520s). From thence (though the sense-leap is less clear) to "solicit votes or test support before an election" (1550s). Compare Old French canabasser "to examine carefully," literally "to sift through canvas." The spelling with a double -s- dates from 16c. and is useful to distinguish it from the other word. Related: Canvassed; canvassing. As a noun, "a soliciting of votes or testing of support," from c. 1610s.