Do you like maple syrup? Of course you do. Everyone loves it. It is made on both sides of U.S.-Canada border, and Canada even stockpiles a reserve of it. The really good stuff comes from north of New York City's most famous and most photographic borough. This cocktail gives you the opportunity to combine that wonderful maple flavor with some tasty brown liquors. It's so easy to mapelize (I know that is not a real word) a Manhattan even I can do it:
2.5 ounces maple bourbon or whiskey (see below)
1 ounce Carpano Antica sweet vermouth
2 dashes Angostura bitters
Combine into a shaker with ice, stir as if you've just come in from the cold (not in the John le Carre sense of the expression as it pertains to spies), and strain into a chilled glass.
Kentucky version -- use Knob Creek smoked maple bourbon
New Hampshire version -- use Cabin Fever maple whiskey
You can't go wrong with either version. It really depends on how much you want a taste of smoke. If you cannot acquire a bottle of either liquor, both of which are quite good, use your favorite bourbon and add a teaspoon of maple syrup.
Regardless of what you use for the bourbon or whiskey (you do know that all bourbon is whiskey but all whiskey is not bourbon, right?) I recommend using Carpano Antica as your sweet vermouth. To paraphrase the hilariously classic line from Spinal Tap, this sweet vermouth goes to 11.