And the Blues are in negotiations with Tom Naylor, Jack Whatmough, Ryan Williams, Craig MacGillivray and Ben Close to remain at Fratton Park.
Cannon is one of five first-team players who is exiting the club as Danny Cowley starts his summer overhaul.
The midfielder moved to Pompey from Rochdale for £150,000 in January 2019 and scored three goals in 79 appearances.
The Blues held the option of an additional year with Cannon but it has not been taken.
Meanwhile, Jordy Hiwula, Charlie Daniels, Bryn Morris and Duncan Turnbull depart along with young keeper Taylor Seymour.
Hiwula netted three times in 15 appearances after arriving on a free transfer in October, while Daniels played 18 times when signing in January from Shrewsbury.
Morris’ time on the south coast unsurprisingly comes to a close, having joined from Shrewsbury in January 2019 and made 29 outings.
He spent the second half of this campaign at Northampton, who were relegated from League One.
Pompey are now in talks with Naylor, Whatmough, Williams, MacGillivray and Close about staying.
All have featured prominently since Cowley was appointed head coach in March.
In addition, the Blues have triggered a clause in Haji Mnoga’s contract to extend his deal for an additional year.
Teenage striker Alfie Stanley has also been offered fresh terms having regularly travelled with the first team this term.
Alex Bass, James Bolton, Lee Brown, Ronan Curtis, Paul Downing, Reeco Hackett-Fairchild, Marcus Harness, Ellis Harrison, Michael Jacobs, Callum Johnson, John Marquis and Sean Raggett all remain under contract.
As reported by The News, scholars Harry Kavanagh, Eoin Teggart, Gerard Storey, Harry Anderson, Charlie Bell and Harvey Rew will leave.
Leon Pitman and Tom Bruce are also departing after Pompey helped them back to full fitness after injury.
What’s more, Harrison Brook and Seok Jae Lee have both turned down extensions to remain in the youth ranks.
It’s understood Brook recently had a trial at Southampton under-23s and Lee with Brentford's B team.