In large heavy saucepan, stir together sugar, corn syrup and water. Bring to boil over medium heat; cook, without stirring but brushing down side of pan with pastry brush dipped in cold water, for about 10 minutes or until candy thermometer reaches 234°F (112°C), or soft-ball stage when 1 tsp (5 mL) hot syrup dropped into cold water forms soft, pliable ball.
Stir in butter and salt cook for about 10 minutes or until 300°F (149°C), or hard-crack stage when 1 tsp (5 mL) hot syrup dropped into cold water forms hard brittle threads. Remove from heat. Stir in vanilla. Stir in baking soda. Stir in Brazil, cashew and macadamia nuts.
Immediately pour onto greased baking sheet. Using greased spatula, spread thinly over pan. Let brittle cool. Break into pieces.