He would be a great upgrade for a team that has to win now. Gio has at least a few years left in his prime. Flames need a #1 center. There is a clear and obvious trade that would help both clubs.
Gio and Monahan to Toronto for Tavares and Nylander.
1) This allows the Flames to re-sign Brodie and keep Hanifin while getting younger. Plus with the Chris Tanev signing, Gio is not needed as much, he can easily be replaced by committee and give the C to Tavares. Then the Flames can dump Gaudreau for prospects.
Flames then become a much better team down the middle - Tavares, Backlund, Bennet, Ryan.
2) The leafs can just about get both Gio and Monahan for the price of Tavares. Dump Nylander and it frees up 9M. Monahan would be a great #1 centre for them and having both him and Gio would greatly boost their defensive structure.