In a small bowl, stir together cheese, watercress, and capers.
Using a 2¼-inch round cutter, cut 8 rounds from frozen bread slices and 8 rounds from salmon slices.
Spread ½ tablespoon cheese mixture each onto bread rounds. Top each with a salmon round, pressing evenly, if needed, to smooth cheese mixture underneath.
Let bread thaw for 5 to 10 minutes before serving, or cover with damp paper towels, place in a covered container, and refrigerate for a few hours until serving time.
Just before serving, garnish with watercress and capers, if desired.
Notes
*We used Boursin.
To give cheese mixture layer a clean edge, canapés can be assembled individually inside cutter, cleaning cutter after each use.
Recipe by TeaTime Magazine at https://teatimemagazine.com/smoked-salmon-boursin-canapes-recipe/