Canvas, with one s, is always a noun. It refers to (1) a heavy, coarse, closely woven fabric used for tents and sails; (2) a piece of such fabric on which a painting is executed; (3) a fabric of coarse open weave, used as a foundation for needlework; and (4) a background against which events unfold.
Canvass, with two s‘s, has a few rare noun meanings, but it is most often used as a verb. Its main definitions are (1) to examine carefully or discuss thoroughly, (2) to go through an area to solicit votes, and (3) to conduct a survey.
Apps Blog has been canvassing opinion on what features such as the new A5 processor and dual cameras … [The Guardian]
Spaetzle is basically a blank, buttery canvas that will absorb whatever flavorings you care to mix into it. [New York Times]
A council in Melbourne’s inner north will canvass the local community about whether or not to ban smoking in public areas. [ABC Online]
Mr Milne has been turning buildings and other structures into digital canvases since establishing his company in 1997. [The Canberra Times]
Police were searching for a missing vehicle and 16-year-old child, and found the two during a canvass of the neighborhood around 1:30 a.m. [NJ.com]