In cocktail shaker, muddle cherries, bourbon, orange liqueur, simple syrup, lime juice and bitters with a muddler or wooden spoon handle. Fill shaker halfway with ice cubes; cover and shake vigorously.
Fill two (8-oz.) glasses with ice; strain bourbon mixture into glasses. Top with seltzer; garnish with cherries and lime wedges.
*To make simple syrup:
Stir a 1:1 ratio of sugar to water in a small saucepan (i.e., 1 cup sugar to 1 cup water). Heat the sugar mixture just to boiling, then reduce the heat and let it simmer until the mixture is clear; do not stir.
Similar to a pestle, a muddler is a long stick used to mash fruits, herbs and spices in the bottom of a cocktail shaker or glass.