Kaneohe Bay is nearly always calm, especially in the mornings. Great place to have a meditative paddle on the glassy water, with wide views of Kaneohe and Oahu's steep, green mountains. There aren't many boats or people on the water, so it's a nice, peaceful experience.
Stand Up Paddleboards can be rented in the nearby town of Kailua at various watersports shops. Kayaks can also be rented as another option. The bay can be reached by public access points in neighborhoods at Kaneohe Bay (there are 3 on Mikiola Drive) or at Kaneohe Beach Park.
Rental Options:
Kailua Beach Adventures
Sammy's Aloha Watersports