Visit comes as Kyiv is on the defensive amid flagging Western aid and Russian territorial gains.
Von der Leyen, Trudeau, Italian Prime Minister Giorgia Meloni, and Belgium Prime Minister Alexander De Croo arrived in the country on Saturday on an overnight train from neighbouring Poland.
Meloni, whose country is chairing the G7 this year, is scheduled to host a video conference on Saturday between leaders from the group of major economies and Ukrainian President Volodymyr Zelenskyy, with new sanctions against Russia and joint arms purchases for Ukraine among the likely topics of discussion.
“More than ever, we stand firmly by Ukraine. Financially, economically, militarily, morally. Until the country is finally free,” von der Leyen said in a post on X.
Trudeau said that Ukrainians were fighting for “our collective future”.
“They are fighting to remind the world that democracy is both important enough to die for and strong enough to win,” he said in a statement before arriving in Kyiv.
“As the war continues, that is what is at stake. And that is why Canada has stood with Ukraine since day one.”
The Western leaders’ visit comes as Ukraine marks the second anniversary of Moscow’s invasion on the defensive amid flagging Western aid and Russian territorial gains.
Kyiv’s fortunes have suffered in recent weeks amid shortages of military supplies, with Russia this month capturing the eastern town of Avdiivka in its biggest victory on the battlefield in months.
United States President Joe Biden has blamed Republicans in Congress for holding up a $61bn package of military funding, casting the support as crucial to Kyiv’s efforts to repel Moscow.
Biden on Friday announced further sanctions against Russia, pledging to keep up pressure on Russian President Vladimir Putin’s “war machine”.
On Friday, Ukrainian foreign minister Dmytro Kuleba delivered a rebuke to sceptics who doubt Kyiv’s ability to defeat Moscow, insisting that “Ukraine will win the war” and victory would come “sooner rather than later” with international support.
Zelenskyy earlier this week told diplomats in an emotional address that he remained “convinced that victory awaits us”.
While neither Ukraine nor Russia has provided official estimates of the number of people killed and injured in the war, both sides claim to have inflicted heavy losses.
The New York Times in August cited US officials who estimated that about 70,000 Ukrainian troops had been killed and a further 100,000-120,000 wounded.
In December, leaked US intelligence suggested that about 315,000 Russian troops had been killed or injured.