Brain's funeral service will start at 11am, and his family have asked as many people to attend, wearing Cherry and White shirts, rugby shirts or bright colours if possible.
A service for family and close friends will follow at Gloucester Crematorium.
A wake will subsequently be held at Kingsholm following the funeral service at the Cathedral.
A book of condolence will also be held at Kingsholm until the end of next week, and there will be another at the funeral service.
The Brain family have asked for charitable donations to be made to the Rugby Football Foundation, the RFU's charity that supports community amateur rugby in England.
Donations can be made directly to the charity, or through Goodwins Funeral Services, Longlevens.
Former Gloucester lock Brain died suddenly on Sunday, May 27th at his home.
Brain balanced a career at Gloucester Trading Standards with racking up nearly 300 games for the Cherry and Whites.
After a stint at Bedford he returned to Kingsholm to coach alongside Phillipe Saint-Andre, before guiding Worcester Warriors to the Premiership for the first time as director of rugby at Sixways.
After a stint as forwards coach at Bristol Rugby, Brain returned to Gloucester in December 2010 as a scout, before assuming the rugby operations and scrum coach roles in summer 2011.
Former Worcester captain Pat Sanderson will be among those paying tribute to Brain at the funeral service.
