Ryan Nugent-Hopkins and Oscar Klefblom scored, and Koskinen made 24 saves for Edmonton (20-16-4), which has lost three of four and enters the Christmas break 2-6-1 in its past nine games.
"Obviously, we just couldn't close it out,'" said Oilers center Connor McDavid, who had one assist. "A bit of a lucky break there on their shot and it goes off the guy's skate, and maybe he kicks it, maybe he doesn't, I don't know.
"But then we have a chance on the power play and we don't score, and they get a chance on their power play and they score, and that's the difference."
Hughes' goal came after the Oilers were penalized for too many men on the ice.
"Connor just jumped too early. Jumped two seconds too early," Oilers coach Dave Tippett said. "It's the details of winning. If you are not willing to do them enough, you're going to lose some games and that's what happened tonight."
Motte's first goal of the season at 11:15 of the first period gave the Canucks a 1-0 lead.