Line 2 sheet pans with waxed paper, then set aside.
Add the popcorn, bacon, pretzels and nuts to a large bowl. Mix and set aside.
Add the sugar, butter, maple syrup, corn syrup and salt to a large, heavy-bottomed pot fitted with a candy thermometer and place over a medium-low heat. When the butter has melted, stir together, then turn up the heat to medium-high. Cook, stirring occasionally, until the candy thermometer reads "hard-crack stage" (300 degrees F), 4 to 5 minutes.
Remove from the heat and stir in the maple extract. Carefully pour over the snack mix and toss using two wooden spoons. Transfer to the prepared sheet pans and spread out to allow it to cool, about 10 minutes. Break into clusters and transfer to a large serving bowl.