In a medium saucepan, bring maple syrup, brown sugar, corn syrup, and salt to a boil over medium heat, stirring until sugar dissolves. Continue boiling 1 minute, reducing heat as neded to prevent mixture from boiling over. Remove pan from heat. Add bourbon, then butter; whisk until butter melts. Let cool to lukewarm, whisking occasionally, about 20 minutes.
Spray a 9-inch glass pie plate with nonstick spray. Unroll the pie crust and line the pie pan; crimp edges. Brush crust with enough egg white to coat. Scatter hazelnuts over the top.
In a medium bowl, whisk the eggs and vanilla until blended. Whisk cooled maple sugar mixture into the egg mixture. Pour mixture over hazelnuts in crust. bake pie in a preheated 350-degree oven until filling is set and slightly puffed, about 50 minutes. Cool completely on rack.
NOTE: Pie can be made 1 day ahead and kept at room temperature, covered.