John Connelly's body was pulled from the water at Speirs Wharf, Glasgow, on Monday July 22 last year.
His family had reported the 28-year-old missing a week earlier when he failed to return to his home in the nearby Milton area from a day out with a friend in the city centre.
Police believe Mr Connelly, known by family and friends as Johnny, may have been assaulted at or near an underpass in Garscube Road leading to Speirs Wharf, which left him with injuries to his head and body.
CCTV shows he was in the underpass in the city's Cowcaddens area at around 10.20pm on Monday July 15.
Officers have discovered three men were near the location at around 10.25pm that night and are appealing to them to get in touch as they may have "vital information".
The men are white, aged between 30 and 45 and have Scottish accents.
They were wearing jeans and sports clothing.
In a re-appeal for information around six months on from Mr Connelly's death, which officers are treating as "unexplained", police said not knowing what happened is causing his family "added anguish and sorrow".
Detective Inspector John Morrison said: "I am appealing to these three men to contact us, they may think they don't know anything but I am asking them to let us be the judge of that.
"A small piece of information, which may seem insignificant, could be vital to us as we build up a picture of what has happened.
"I am also re-appealing to the public to consider whether they too have information which could be relevant.
"Anyone losing a loved one is entitled to know what happened to them. Please contact us and pass your information on.
"Johnny was a loving son, brother and a much loved uncle. His family is still trying to come to terms with his loss and just want to know what happened to him.
"Not knowing what happened or how he came to his death is causing them added anguish and sorrow.
"We remain committed to finding out what happened to Johnny and finding answers for the family devastated by his death."
Officers have combed through hundreds of hours of CCTV footage, taken more than 50 statements and carried out a stop and interview operation at the canal as they try to piece together Mr Connelly's movements before his death.
Anyone with information is asked to call CID officers at Maryhill Police Station via 101, quoting incident number 3452 of July 22.