When you open a Level Sequence asset UAssetDefinition_LevelSequence is used.
Inside FLevelSequenceEditorToolkit::Initialize FSequencerModule::CreateSequencer is called. Which eventually calls FSequencer::InitSequencer.
Important params are passed to FSequencer::InitSequencer like callbacks for object bindings (check Sequencer Editor Add Actor Track for more details on what is happening when you want/add an actor binding track).