Vancouver is the third NHL stop this season for Spooner, who has also played for the New York Rangers and Oilers.
The Oilers said on Twitter they hoped Gagner would be available for Saturday night's game against the New York Islanders.
The 27-year-old Spooner had one goal and one assist in 16 games with the Rangers and two goals and an assist with the Oilers. He also spent time with Bakersfield of the AHL. He was drafted by Boston in the second round in 2010.
The 29-year-old Gagner has spent most of the season on loan to Toronto of the AHL, totaling 12 goals and 25 assists. He was selected No. 6 overall in the 2007 draft by Edmonton and spent his first seven NHL seasons with the Oilers.