For the whiskey sauce: Combine the heavy cream, maple syrup, corn syrup and salt in a medium saucepan and stir. Cook over medium-low heat, stirring constantly, until the sauce has reduced and thickened, about 25 minutes. (The sauce should bubble slightly as it's cooking). Stir in the whiskey and take off the heat.
Pour into a container and let cool to room temperature, then refrigerate until completely chilled, about 2 hours.
For the candied bacon: Preheat the oven to 350 degrees F.
Set a wire rack on a rimmed baking sheet and lay the bacon slices on the rack. Microwave the maple syrup and brown sugar together in a small bowl until just melted, 15 to 20 seconds, then stir or whisk to combine. Brush the mixture on both sides of the bacon.
Bake, rotating the pan halfway through, until crisp, about 15 minutes. Remove and let the bacon cool on the rack for a few minutes, then gently lift the bacon off the rack and set it back down. (Doing this will ensure it doesn't stick to the rack when it cools.)
For the sundae: Using a 2-ounce scoop, put 3 scoops of ice cream in a dish. Drizzle some of the chilled maple whiskey sauce over the ice cream. Cut a slice of bacon in half and arrange in the dish. Top with the chopped toffee bars. Repeat 5 more times and enjoy!