Trainers » Guzma
If I play "Guzma", who chooses which Pokemon to switch for each player?
You make all of those choices.
Source: Burning Shadows FAQ (2017-07-20), TPCi Rules Team (2017-08-03)

Relevant cards

Note: All applicable cards may not be listed below.
SM3_115
SM3_115a
SM3_115a
SM3_143
SMA_SV84
SMA_SV84