Hi there, no official river sup in Bali, but the rafting trips are great and the scenery is awesome. Sanur is a nice spot, the waves can be okay but your right on reef. Take some booties, makes a big difference. Try taking a trip to either canggu or nusa lembongan.
Both have better waves than sanur this time of year and your not right on top of the reef.
Good luck and have fun