Brunch is not a utilitarian meal one eats to fuel themselves for the day, unless that day involves a nap. Booze is an expected part of brunch, but it usually comes in a glass, either paired with orange juice or Bloody Mary mix. Those are both good ways to enjoy booze at brunch, but you can eat your booze too. I like to eat mine in French toast.
There are multiple ways you can do this. You can add it to the toast itself, and mix a couple of teaspoons (or tablespoons) of your favourite spirit into the custard—just like you would vanilla—or you can add it to a topping, such as whipped cream or syrup.
If you are going to make a boozy syrup, try the one from Binging with Babish. Babish combines half a cup with maple syrup with a tablespoon of butter and a quarter cup of rum, then lets it reduce on the stove to form a thick syrup. (This template also works for non-rum boozes.) For whipped cream, you can add up to a tablespoon of alcohol per cup of cream, then whip as you usually would until soft peaks form.
Most recipes suggest dark spirits for boozy French toast—The Kitchn loves Irish whiskey here, for example—but this is a good opportunity to raid your bar cart for inspiration. Rum is a good choice, but pineapple rum is a bit more fun (and tropical). French toast is also a good vehicle for those last few splashes of liqueur or amaro, particularly anything of the hazelnut, chocolate, or fruit variety. (Vanilla-infused Fernet would be pretty good, too.)
Feel free to mix and match, and infuse multiple components with the good spirit. Bourbon-spiked French toast drizzled with cherry kirsch syrup sounds pretty excellent, as does pineapple rum toast with coconut rum whipped cream. Let the creativity flow, along with the alcohol, is what I’m saying. Short of pouring unadulterated gin onto a pile of fluffy French toast squares, there are very few ways to screw this up.