Shelina Zadorsky of London, Ont., Jaclyn Sawicki of Coquitlam, B.C., and Catherine Charron-Delage of Longueuil, Que., also scored for Canada.
Goalkeeper Sabrina D'Angelo of Welland, Ont., got the shutout for Canada, which is aiming to build on the success of the bronze medal performance by its senior team at the London Olympics.
Argentina was reduced to 10 players for most of the game after Agustina Barroso was sent off in the sixth minute.
North Korea edged Norway 4-2 in the other Group C match Monday.
Canada's next match is Thursday against Norway.
In Group D play Monday, the U.S. beat Ghana 4-0 while Germany shut out China 4-0.
The top two teams from Group D will face the top two teams from Group C in the quarter-finals Aug. 31.
In Kobe, Kim Un Hwa and Kim Su Gyong scored in the second half to lead North Korea over Norway.
Yun Hyon Hi scored first, heading in Kim Un Hyang's cross in the 15th minute. Norway levelled eight minutes later through Caroline Hansen's superb finish from just inside the box.
North Korea made it 2-1 five minutes before the break when Yun was taken down in the area by Ida Aadalen and scored on the resulting spot kick.
Ada Hegerberg pulled Norway level after the break, but two goals in a span of five minutes by Kim Un Hwa and Kim Su Gyong ensured victory for North Korea.
Maya Hayes scored a hat trick to lead the American attack in Hiroshima.
The Americans took a 1-0 lead when Morgan Brian's header hit the crossbar and bounced in after hitting Ghana defender Kinda Addai for an own goal in the 20th minute.
Hayes doubled the lead five minutes into the second half, heading in a cross from Kealia Ohai, and made it 3-0 in the 74th with a right-footed shot from just outside the box.
Hayes completed her hat trick two minutes into injury time when she chipped goalkeeper Patricia Mantey to score her 15th goal in international play.
"It's always exciting to come into an atmosphere like this," Hayes said. "It was great to get three goals, but I couldn't have done it without the help of my teammates. This team brings out the best in me."
The United States, one of the tournament favourites, is looking to build on the success of its senior women's team that won the gold medal at the London Olympics.
"We came away with the result we wanted today and I couldn't be happier for Maya," U.S. coach Steve Swanson said. "She has worked very hard and showed the explosiveness she has."
The Americans, who won this tournament in 2002 and 2008, will next face China on Aug. 23 before wrapping up group play against defending champion Germany on Aug. 27 in Miyagi.
Germany also made a strong start in Group D. Lena Lotzen scored in the third minute, and Anja Hegenauer doubled the lead in the 45th. An own goal from Lin Yuping and an injury-time strike from Luisa Wensing gave the defending champions a comfortable win.
— With files from The Associated PressSuggest a correction