Port on top complements the maple syrup, and although this is a bit sweeter than for all tastes it's quite balanced. Obviously, you can dial the lemon...
A fantastic cocktail - rye with lime and maple syrup is wonderful. The frothy egg white is attractive and helps keep the drink mouthfeel light. And the port is fantastic - not only visually appealing it extends the depth of the flavor (similar to a New York Sour vs. a regular whiskey sour). A great cocktail - congratulations!