Mr. Trudeau said "we are going to defend our industries and our workers" and "show the U.S. President that his unacceptable actions are hurting his own citizens".
Other G-7 leaders, including British Prime Minister Theresa May and German Chancellor Angela Merkel, have also spoken out against the tariffs.
USA stocks, apart from those of steel and aluminum producers, have fallen sharply in response to Trump's recent tariff announcements and other actions against trading partners.
The Canadian leader is embroiled in a row with Washington over negotiations to revamp the nearly 25-year-old the North American Free Trade Agreement, as well as over the steel and aluminum tariffs. At last year's G-7 summit in Sicily, Macron said he could talk the US out of withdrawing from the climate accord.
Macron said he has tried in vain to convince Trump to change his positions on various issues like climate change, Iran and trade, but said ultimately he can't make decisions for the US president.
He, along with other G7 leaders, say they will demand Trump reverse the duties when they meet him during the summit, which begins Friday in nearby La Malbaie. She has had frosty relations with Trump in the past. But officials have conceded the G7 agenda is likely to be overtaken by trade disputes.
They also renewed their commitment to the fight against climate change and to promote democratic values, free and open trade, and gender equality.
"The G7 is an opportunity for us to get together and have frank, open discussions among nations who have always been allies and friends", Macron told reporters, with Trudeau at his side. Japan has said it can not normalize diplomatic relations without the issue's being resolved.
The G7 developed in part because the world's rich powers - despite their Cold War victory - became frustrated working through the broader multilateral system with lesser rivals.
The relationship has reportedly frayed to the point where Trump was considering sending Vice President Mike Pence to the G7 summit in his place, according to a Washington Post report.
Numerous attending members have expressed displeasure with Trump's tariffs last week. Trudeau recently said Washington's new import tariffs were "insulting".
Protesters rally ahead of the G7 leaders' summit. Trump may have less to fear than slow-growing Europe and Japan from a trade war in terms of economic losses if the "G6" pushes back on tariffs. "Finance Ministers and Central Bank Governors requested that the United States Secretary of the Treasury communicate their unanimous concern and disappointment".
"The United States must, at long last, be treated fairly on trade", the President tweeted on Saturday.