As the name suggests pear and almond are the main flavours with calvados providing backbone and hints of apple, while champagne dries and adds effervescence
Normally, I would strain ingredients into a chilled glass then add the Champagne, but that’s not how your directions read. You really want the Champagne to go into the glass first and the strained ingredients go on top of the champagne?
Pouring the shaken ingredients over the sparkling wine helps mix the cocktail and saves the need to briefly stir to combine - any stirring inevitably affects fizz. Also pouring over the sparkling wine also means the wine does not fizz up as much.