The midfielder's Pompey arrival is waiting to be rubber-stamped by the Football Association, following the opening of the January transfer window.
Still, the Â£150,000 purchase from Rochdale has linked up with his new club ahead of ratification.
Cannon, however, is unavailable for Saturday's trip to Norwich as he is cup-tied, having featured against Pompey in the FA Cup during the previous round.
He is also ruled out of the Checkatrade Trophy visit to Southend (January 8), after facing Fleetwood in the competition.
Kenny Jackett, though, is anticipating the 22-year-old being available for the League One visit of Blackpool to Fratton Park (January 12).
The Blues bossÂ said: '˜Cannon is available as we stand now.
'˜He wasn't available against AFC Wimbledon,Â but paperwork '“ for whatever reason '“ gets done on January 2.
'˜He has played in the FA Cup and Checkatrade Trophy, so his first available date will be January 12 against Blackpool.
'˜At least it gives him a couple of weeks to train with us.'
Cannon appeared as a 55th-minute substitute in Rochdale's 1-0 defeat to Pompey in the FA Cup last month.
Andre Green's last-gasp winner clinched a second-round victory for Jackett's men '“Â who now face Norwich.
Meanwhile, his sole goal so far this season arrived in the Checkatrade Trophy.
That came in a 2-0 win at Fleetwood in October '“Â Cannon's last 90 minutes for the Dale.
It was also his final appearance in the competition, despite Rochdale's ongoing progress. Nonetheless, he remains cup-tied.
CannonÂ represents Pompey's first piece of business during the January transfer window.
Jackett is also keen toÂ strengthenÂ his striking options and the central-midfield areaÂ during the next month.
Chief executive Mark Catlin has already stressed there won't be widespread changes for the long-time League One leaders.
And Pompey's boss has reiterated a fine-tuning process will be carried out.
Jackett added: '˜Hopefully the ones we do get will be key. I don't think there will be a massive turnover, but more key ones than numbers definitely.
'˜We want ones that make a difference, like everybody. Ones that can either enhance us or plug a gap if it comes about.'
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