Gagner, 29, will rejoin the team that drafted him with the sixth overall selection in 2007. The London, Ontario native played his best hockey in Edmonton, reaching the 40-point mark in each of his first five seasons with the club.
The 5-foot-11 winger has spent the majority of the campaign on loan with the Toronto Marlies of the AHL and is in the second of a three-year contract with Vancouver. His deal has an annual cap hit of $3.15 million.
Gagner won't have to wait long for his chance in Edmonton, as the team announced that defenseman Matt Benning has been placed on injured reserve. The move clears a roster spot for Gagner to join the lineup against the New York Islanders on Saturday.
Spooner, 27, was acquired by Edmonton on Nov. 16 from the New York Rangers. It's been a trying season for the centerman, who's tallied three goals and five points through 41 games between the two clubs this year.
The Ottawa, Ontario product is in the first of a two-year contract with an annual cap hit of $4 million.