Officers were called to the Boulters Bar and Restaurant complex following reports of a 'disturbance' shortly after 11pm on Wednesday.
A man was taken to hospital but died at about 6am yesterday.
The men, aged 22, 24 and 29, have been bailed until late January.
An 18-year-old woman also arrested on suspicion of murder has been released without charge.
A post-mortem examination has been carried out on the man, who has still not been formally identified by police, but was unable to establish a cause of death.
The bar and restaurant, which are situated on the island off Ray Mead Road, are set to re-open today.
The investigation continues.
Contact police on 101 or Crimestoppers on 0800 555111 with information.Report 4: Boulters Lock murder investigation: Bar and restaurant to re-open
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The victim of an assault in Cippenham was flown to hospital by air ambulance this afternoon.
A rapid response vehicle, an ambulance officer, an air ambulance and an ambulance crew were all called to an address in Earls Lane at 2.10pm.