"Canada grieves with our Swedish friends in this hard time and we offer all possible assistance", the prime minister said in his statement on Friday.
While the suspect behind the attack has not been named, Swedish police told The New York Times Saturday that they had arrested a 39-year-old Uzbekistan-born man Friday evening in alleged connection. "We know that he showed sympathies for extremist organisations, among them ISIS", national head of police operations Jonas Hysing told reporters.
Hysing explained: "The Migration Agency rejected it in June 2016 and also decided that he was to be expelled".
A terror ramming attack Friday that left four people dead and 15 injured in Stockholm could have been worse, according to Swedish police.
The truck, hijacked from a beer company, was driven into Ahlens department store in the capital on Friday afternoon. Earlier the authorities said seven people had been brought in for questioning.
However, police said they were ever more convinced that the Uzbek man was the driver of the commandeered truck and may have acted alone.
He had been seen only as a "marginal character", National Police Commissioner Dan Eliasson said.
The Ahlens store cancelled a planned half-price sale of smoke-damaged goods on Sunday and apologised to customers after a storm of protest on social media that such a step would be disrespectful to the attack victims.
Sweden authorities have yet to identify the names of the killed, but The Associated Press breaks down the deceased as including two Swedes as well as a British man and a Belgian woman.
Police say the man was known to have expressed sympathy for groups including so-called Islamic State.
There was no immediate claim of responsibility for the attack.
Police had found a suspect device in the cab of the lorry.
Sweden's health service raised the number of people being treated in hospitals for injuries to 10.
Sweden's Prime Minister Stefan Lofven says Swedes "must get through this".
Today thousands of people gather in Stockholm to show that peace and love will win over violence and hate. In December 2010, a suicide bomber blew himself up, also on the Drottninggatan street, slightly injuring several passersby.