On Thursday late-afternoon, Damian Cox of the Toronto Star reported that a deal was being finalized.
Sources later confirm that same information to TFP, and indicated that Shanahan was not simply coming on as President of Hockey Operations, but President of the Leafs' entire organization.
TFP has learned that Shanahan will be leaving his position with the NHL as its Director of Player Safety on Friday, upon which the Leafs will announce his hiring.
A formal introduction, however, will be made at a press conference next week.
According to the Star, Leiweke has had interest in Shanahan for months, and talks picked up over the coming weeks.
Maple Leafs GM Dave Nonis is expected to remain on board as GM of the club, while a decision on the future of head coach Randy Carlyle will be made collectively, though one source close to the Leafs told TFP there is a good chance the bench boss will be back for the 2014-15 season.
Several roster moves, however, are likely this off-season, as it's believed the Leafs will look to trade the likes of center Nazem Kadri and goalie James Reimer, among others.
Pending unrestricted free agent forward Nikolai Kulemin is not expected to be re-signed, while UFA-to-be center Dave Bolland's contract demands may be too much for the Leafs to accept.
Since retiring from hockey in 2009, Shanahan served at the NHL's VP of Hockey and Business Development through 2011, upon which he jumped into his current role with the League.
Drafted second-overall by the New Jersey Devils in the 1987 NHL Entry Draft, the native of Mimico, Ontario, won three Stanley Cups, all with Detroit, in 1996-97, 1997-98 and 2001-02.
In 1,524 career NHL regular-season games with the Devils, St. Louis Blues, Hartford Whalers, Red Wings and New York Rangers, Shanahan accumulated 656 goals (putting him 13th in NHL history) and 698 assists for 1,354 points, along with 2,489 penalty minutes.