The downing of a Ukrainian airliner carrying at least 63 Canadian citizens could encourage collaboration between President Donald Trump and Canadian Prime Minister Justin Trudeau as their governments investigate the incident – even though the two leaders haven't always seen eye to eye.

U.S. and Canadian officials said the Ukrainian International Airlines flight was downed by an Iranian surface-to-air missile late Tuesday near Tehran, Iran, killing all 176 passengers aboard.

Iran disputes shooting down the plane and has called on Canadian and U.S. investigators to release evidence of a missile.

Although some of Trump's critics have suggested the plane was "collateral damage" amid an escalation in U.S.-Iran tensions, Trudeau has said it was "too soon" to draw any conclusions.

When asked by reporters at a Thursday press conference if he thought the Soleimani strike led to the downing of the jet, Trudeau replied, "I think it is too soon to be drawing conclusions or assigning blame or responsibility in whatever proportions."

More:Iranian missile likely caused Ukraine plane crash, Pompeo says; Ukraine gets access to black box

More:Iran got its revenge for Qasem Soleimani's killing but the US Navy is still a target

Although Trudeau initially spoke positively of Trump, the two leaders have often sparred. Here are some of the high and low points from their relationship over the past several years:

'He's authentic'

In an interview with The Skimm in August 2017, Trudeau said Trump was "authentic," making it possible to work with him.

"It may be surprising to some that he's authentic, in that the person he is on camera in public is very true to the person he is in private," Trudeau said at the time.

As time went on, though, their relationship became testier.

'Meek and mild'

Following disagreements at the Quebec G-7 conference in June 2018 over a joint statement with other world leaders documenting the meeting and agreements, Trump called Trudeau "meek and mild" on Twitter.

'Completely unacceptable'

Trudeau weighed in on Trump's controversial "send her back" chant at a July 2019 rally, calling the remarks “hurtful, wrong and completely unacceptable.”

During Trump's rally in North Carolina, after he denounced Rep. Ilhan Omar, D-Minn., the crowd started chanting "send her back," a reference to Trump's tweets about freshmen progressive lawmakers needing to "go back" to other countries. Omar came to the United States as a refugee and is a naturalized U.S. citizen.

More:Canadian Prime Minister Justin Trudeau slams 'send her back' chant at Trump rally as 'completely unacceptable'

'Two-faced'

After a viral video circulated showing Trudeau and other world leaders appearing to laugh at Trump at the 2019 NATO summit in London, Trump called Trudeau "two-faced" while talking to reporters after a meeting with German Chancellor Angela Merkel.

More:Trump calls Trudeau 'two-faced' following video of NATO leaders appearing to gossip about him

Controversy over 'Home Alone 2'

In response to reports that a cameo with Trump had been cut from Canadian broadcasts of "Home Alone 2," Trump tweeted "I guess Justin T doesn’t much like my making him pay up on NATO or Trade!"

What's next

Despite their past differences, Trump administration officials indicated they would work with Canadians to investigate the plane crash.

Speaking at a press conference announcing new sanctions on Iran, Secretary of State Mike Pompeo said he had discussed American actions with his Canadian counterpart, and Treasury Secretary Stephen Mnuchin said the Treasury Department would issue waivers for all who could assist in the investigation into the jet's downing.