Canvas is a thick cotton cloth, the kind Van Gogh painted Starry Night on. Add an "s," and to canvass is to go door to door discussing your favorite politician with your neighbors.
A blank canvas is a painting waiting to happen. Canvas is a great material to paint on because it's light and sturdy. Canvas can also be used to make sails, shoes, tote bags, tents, and more! Check out these examples of the word:
She stumbled backward, her eyes wide, as the figure started coming out of the canvas. (Pet)
The shoes in the corner were all old-fashioned black or brown leather, except for one pair made from canvas and covered in dried mud. (The Marvels)
The canvas tore even further, the tattered material flapping wildly. (The Martian)
The word canvass, on the other hand, means to take a poll, to ask people questions and get their opinions. You might canvass your neighborhood for a politician you support by discussing elections and asking people to vote. Here is canvass in action:
After the intro, the politicians canvass the audience, seeking donations. (Washington Post)
My responsibilities were to organize the campaign, coordinate the regional branches, canvass for volunteers, and raise funds. (Long Walk to Freedom)
Together they canvassed the sidewalk outside their building on 141st Street, equipped with clipboards and pens. (The Vanderbeekers of 141st Street)
Bonus! Behold a sentence with both words:
A canvas is to an artist what a canvass is to a pollster. (Woe Is I)
To remember the difference, canvass has a double "s" because people often canvass on the street and sidewalk.