Yes there are trout, but its a big river. I have only ever fished the middle Rakaia for Salmon, but on other braided rivers I have found veltic style lures to work very well, cast upstream then retrieve. I like striped orange and black ones.
Also could try Rapala’s or other minnow lures, ones which dive or sink are probably the best option. When the river is clear go for a natural colour, but if its milky then consider going bright.