"This tragedy should have never occurred, and I want to assure you that you have my full support during this extraordinarily difficult time... You give us purpose to pursue justice and accountability for you," the BBC quoted Trudeau as saying on Sunday while addressing a vigil Edmonton, Alberta for the 57 Canadians killed in January 8 disaster.
"We will not rest until there are answers," he added.
Trudeau attended the memorial on Sunday, as a second day of anti-government protests against Iran's leaders erupted in Canada and abroad.
On Saturday, Iran's Islamic Revolutionary Guard Corps admitted that one of its missiles had downed the Kiev-bound Ukraine International Airlines (UIA) flight PS75 on January 8, killing all the 176 people on board.
It said Iran was on "high alert" that day because of the US threats of possibly hitting 52 spots in the country, the operator of the missile launch site was concerned about a possible "US cruise missile".
The crash occurred on the same day Iran launched more than a dozen ballistic missiles at two US military bases in Iraq, in retaliation for the killing of Iranian Major General Qasem Soleimani in an American drone attack in Baghdad on January 3.
Following Iran's admission on Saturday, Trudeau had said that there must be a full investigation with "full clarity on how such a horrific tragedy could have occurred".