The Collaborative International Dictionary of English v.0.48:

Canvass \Can"vass\, v. t. [imp. & p. p. canvassed; p. pr. &
   vb. n. Canvassing.] [OF. Canabasser to examine curiously,
   to search or sift out; properly, to sift through canvas. See
   Canvas, n.]
   1. 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.
      [1913 Webster]

            I have made careful search on all hands, and
            canvassed the matter with all possible diligence.
                                                  --Woodward.
      [1913 Webster]

   2. To examine by discussion; to debate.
      [1913 Webster]

            An opinion that we are likely soon to canvass. --Sir
                                                  W. Hamilton.
      [1913 Webster]

   3. To go through, with personal solicitation or public
      addresses; as, to canvass a district for votes; to canvass
      a city for subscriptions.
      [1913 Webster]

WordNet (r) 3.0 (2006):

canvassing
    n 1: persuasion of voters in a political campaign [syn:
         electioneering, bell ringing, canvassing]