Heavily-pregnant Samia, 27, who plays hairdresser Maria Connor in the soap, was with her property developer husband Matthew Smith when they made the find.
They had gone to investigate a dog's desperate barking from inside the van.
Samia and husband Matthew discovered the dead man on Sunday afternoon in Sale, Greater Manchester, when they investigated a barking dog
The couple, who were visiting Samia's family in Sale, Greater Manchester, saw the body through the back window of the red Vauxhall Combi and dialled police.
Officers closed the road and sealed off the van under a tent.
They were stopped from getting into the van by the dog, a Staffordshire bull terrier, which had to be taken away by vets.
Forensic investigators carried out detailed searches as shocked neighbours looked on. Police said the body was of a 26-year-old man from nearby Northern Moor.
His death is being treated as suspicious. Coronation Street confirmed that Samia and her husband - who are expecting their first child next month - discovered the body and reported it to police, but refused to comment further.
Police forensic officers pick up clues from the van after the body was discovered by the Coronation Street star
A spokesman said: 'It is a police matter.'
It is understood that both Eccles-born actress Samia and her husband were asked for their accounts of their discovery by officers, in line with procedure.
Police said they were called to Hunston Road, off Washway Road in Sale, shortly after noon on Sunday.
Neighbours said the van had been parked on the quiet, tree-lined road outside a newly-built block of flats all weekend.
It is understood that there were no injuries on the man's body. Police are now awaiting the results of toxicology tests.
Officers were last night informing his next of kin and have not yet released his name. It is understood he had borrowed the van from its owner.
One neighbour, who asked not to be named, said: 'It has been parked here since Friday and the dog's barking was very loud and went on for quite a while. We have never seen the van before and don't know who owns it but it is very sad.'
Police said that they were following several lines of enquiry but did not yet know the cause of the man's death. A post-mortem examination is due to be held.
Samia, who joined Coronation Street in 2000, married Matthew in Chester in 2005 after a seven-month engagement. They live in Cheshire.
She was devastated in April after the death of her father Joseph from cancer.