Blake Lizotte and Arthur Kaliyev each had a goal and an assist, and Anze Kopitar had two assists for the Kings (45-22-10), who were coming off a 3-1 win at the Seattle Kraken on Saturday. Joonas Korpisalo made 24 saves.
"I don't want to say it's a relief, because we've sensed that's been coming, but once you get that asterisk by your name you can breathe a little bit," Los Angeles coach Todd McLellan said. "That's a [heck] of an accomplishment for our group."
The Kings also moved one point ahead of the Edmonton Oilers for second place in the Pacific Division, one point behind the Vegas Golden Knights.
"A good feeling," Kopitar said about clinching a berth. "Second year in a row. That's a sign that the team is trending in the right direction, and we like where we're at, but we still have five games, so got to focus on those and make sure we're sharp going into the playoffs."
Thatcher Demko made 21 saves for the Canucks (34-35-7), who have lost three in a row (0-1-2) and were eliminated from playoff contention when the Winnipeg Jets defeated the New Jersey Devils 6-1 earlier on Sunday.
"We pretty much knew a couple of games ago it was unrealistic to make it," Vancouver forward Elias Pettersson said. "But we still play with pride and try to build for next season. So, these games are important. We have six games left to build."
Brock Boeser put the Canucks ahead 1-0 at 5:56 of the first period on a rebound at the top of the crease.
Iafallo tied it 1-1 at 13:02 during a 4-on-4. He one-timed a cross-ice pass from Kopitar past Demko's outstretched glove from the right circle.
"Just had to hammer it home," Iafallo said.