TORONTO -- A man accused of plotting to derail a Canadian passenger train also thought about triggering a catastrophic volcanic blast in the United States, his trial heard Tuesday.

Testifying for a third week, an undercover FBI agent said Chiheb Esseghaier pondered the possibility of getting the volcano in Yellowstone National Park to erupt.

Esseghaier, who is charged with various terror-related offences along with co-accused Raed Jaser, spoke of the "death and destruction" a blast could cause, court heard.

The Montreal PhD student from Tunisia was "very passionate" about the topic of the volcano in the park, which straddles the borders of Wyoming, Idaho and Montana, the agent said.

"Wouldn't it be great if my enemies' worst national disaster could happen?" the agent cited Esseghaier, 30, as saying.

Ultimately, however, he decided the idea was not feasible.

"No. We cannot do anything to make the volcano erupt. It's very deep. I don't have any access," Esseghaier apparently told the agent.

"It was his conclusion that we need to focus on the project or projects," the agent told Superior Court.

"The train plot was a better bet than the volcano," defence lawyer John Norris, who represents Jaser, said by way of clarification.

The train idea, apparently, had come from "The Responsible One," a man Esseghaier had met in Iran who supposedly had close ties to top al-Qaida leaders.

According to the testimony, the aim was to cut out about five or six metres of rail -- possibly using a military grade laser -- to derail a Via Rail passenger train as it made its way from New York City to Toronto at about 7 p.m. The FBI agent offered construction equipment and uniforms in support of the train plot.

Court heard the plotters scouted suitable sites to damage the rails, including a bridge in east Toronto. Norris, however, noted the New York train actually enters Toronto from the west.

Norris also got the agent to agree that Esseghaier had warned him against discussing the plot with Jaser, 35, a Palestinian dispatcher from Markham, Ont.,

Jaser would later decide a train attack would be too difficult to carry out and dropped out in September 2012.

Another plot the men kicked about -- which Norris said had "some pretty obvious problems" -- involved recruiting a Muslim cook to poison soldiers on a military base, court heard.

Esseghaier even talked to a cook he knew about the idea, but the man stopped taking his calls, court heard.

The agent conceded the plot was a "little fuzzy," saying it wasn't clear whether Canadian or American soldiers were the target.

Police arrested the accused in April 2013.