If you want to start a MIDI sequence, you’ll have to
- insert a media player in your song and load the midi sequence
- Use a binding that is triggered by your pad button and starts the media player
If you want to start something outside Cantabile, it depends how that can be remote-controlled. I prefer MIDI control, so you’ll need a virtual midi connection like loopMIDI, then send out MIDI commands on this connection from Cantabile via bindings that are received by FL studio, listening to your loopMIDI connection. If FL studio is set up accordingly, you can start playback that way (I don’t use FL studio, so can’t help you there).
Not sure what version of Cantabile you are using - availability of media players and bindings depends on Cantabile version.