What is it? = When you "Canvass for guests," it means you're kind of doing a Wi-Fii search for other nearby DQ9 players, usually like you have a friend who's also playing DQ9 or fan-gathering event.
What for? = To share treasure maps with each other. However, the players can only share the maps only after beating that map's dungeon.
Why do it? = Dungeons are great places for leveling up/rare items/etc.
How does it work? = Both you and your friend must be "Canvass for guests" and sort of link up. You'll see each other's characters and may share treasure maps.