What caused Canada to change their stance on the "lab leak" theory of COVID?

Question

On May 27th 2021, Prime Minister Trudeau said:

“We support the call by the United states and others to better understand the origins of COVID-19,” Trudeau told reporters.
“I know there are a lot of theories out there, but we need to make sure we’re getting to a full and complete airing of the facts to actually understand what happened and how to make sure it never happens again,” he added.

However this contrasts with Canada's earlier official position. In May 2020, Trudeau said:

Speaking to reporters on Sunday, Trudeau said Canada has been working with its Five Eyes partners — Australia, New Zealand, the United Kingdom and the United States — on “various” pieces of intelligence regarding the COVID-19 outbreak.

But, he said it is “too early to draw firm conclusions.”

Trudeau said Canada will continue to work with intelligence and allies around the world to “find answers to the many questions people are asking.”

The Five Eyes then prepared a report rejecting this hypothesis:

There is no current evidence to suggest that coronavirus leaked from a Chinese research laboratory, intelligence sources have told the Guardian, contradicting recent White House claims that there is growing proof this is how the pandemic began.

The sources also insisted that a “15-page dossier” highlighted by the Australian Daily Telegraph which accused China of a deadly cover up was not culled from intelligence from the Five Eyes network, an alliance between the UK, US, Australia, New Zealand and Canada.

Afterwards Trudeau was mute on the subject, despite President Trumps and Secretary Pompeos persistent attempts to reopen the subject, up until President Biden expressed his support for a fresh investigation.

What new pieces of information became available over the past year that might have made Trudeau?

Answer 1

This sounds like more of a change in tone than a change in actual stance. That is, the statements you've quoted don't actual conflict. To paraphrase:

1. "There is no current evidence to suggest that coronavirus leaked from a Chinese research laboratory"

2. It's "too early to draw firm conclusions.”

3. "I know there are a lot of theories out there, but we need to make sure we’re getting to a full and complete airing of the facts to actually understand what happened and how to make sure it never happens again."

All those statement are consistent with the broad stance, "it's possible a lab leak was responsible, but right now there's no evidence." That stance put Trudeau in opposition to the Trump administration's stance ("there's evidence that it came from a lab") but not the Biden administration's more neutral stance ("the possibility of a lab leak should be investigated"), so Trudeau is more comfortable lending support to the U.S. position than he was last year.