Although you can make a whiskey sour with bourbon or rye whiskey, the choice is crucial to the drink's flavor. The difference in taste is due to their distinct mash bills.
Bourbon offers a smoother, sweeter, and fuller-bodied flavor with a corn mash bill. You may even detect tasting notes of vanilla, caramel, honey, nuts, and oak from the cask.
If you want sweet but are using rye whiskey, orange juice will give the cocktail a sweeter and slightly tangy twist as it helps balance the rye's spiciness with citrusy notes.