pull up the Mixer (View > Window > Mixer) and there will be a "monitor" button on the either input and output MIDI bus strips;
you'll need to connect the MIDI out of the game (if that has one) to MIDI Master In and the "monitor" trick lets the incoming MIDI stream go all through into the plugin chain in the MIDI Master Out (where you probably have inserted the Roland Canvas VST).
system:playback is usually the main/default sound device speakers, at least on a genuine jackd system; if you're on PipeWire then it probably is named differently eg. "Built-in Analog Audio Stereo" (or something else...)
pull up the Mixer (View > Window > Mixer) and there will be a "monitor" button on the either input and output MIDI bus strips;
you'll need to connect the MIDI out of the game (if that has one) to MIDI Master In and the "monitor" trick lets the incoming MIDI stream go all through into the plugin chain in the MIDI Master Out (where you probably have inserted the Roland Canvas VST).
system:playback is usually the main/default sound device speakers, at least on a genuine jackd system; if you're on PipeWire then it probably is named differently eg. "Built-in Analog Audio Stereo" (or something else...)
hth.