The US President Donald Trump says expelling Russian President Vladimir Putin from the group in 2014, then called G8, was a mistake.
He also said a US-Canada trade deal is achievable, but won't give up his belief in tariffs.
Welcoming G7 members, Canadian Prime Minister Mark Carney said the world is looking at them for leadership and they are at a turning point in history.
It's the inaugural gathering for several key leaders and the first since Trump returned to the White House.
The G7, or Group of Seven, is an informal organisation that includes the world's seven wealthiest democracies.
It was founded in 1975 when France hosted the first meeting.
The current members are the UK, the United States, Japan, France, Germany, Canada and Italy. The European Union is also represented.