The sticking point will be the short ribbon cable between the bonnet and the Pi, the one included in the kit is designed for the smaller camera connector found on the Raspberry Pi Zero, rather than the full sized connector of the Raspberry Pi 3. There are adaptor cables available—the cable connecting the camera module to the Bonnet is one of these after all, and they are available separately—so at least in theory if you pick up one of these you should be able to use the Bonnet with the Raspberry Pi 3. I haven’t tested it however, so YMMV.