Combine first 4 ingredients in a medium saucepan. Cook over medium heat until sugar dissolves, stirring constantly (about 8 minutes). Add pecans and vanilla; cook until all syrup is absorbed and pecans are coated, stirring constantly (about 12 minutes). Spread pecan mixture on a baking sheet coated with cooking spray. (Pecans will have a sugar coating.) Separate pecans into halves. Cool completely.
NOTE: Store in an airtight container in a cool, dark place for up to one month; in the refrigerator for up to 3 months; or in the freezer for up to 8 months.