After the terrible bear attacks on bikers and runners a few years ago, I started carrying bear spray in my bottle cage. The method that works for me is placing a spray bottle and holster in the cage and strapping the holster to the tube. A beer koozy might also work to hold a spray can, especially one in a holster, in the cage without a strap.
Wendy uses a water bottle to hold her bear spray. We'll try to get photos of that option, too.
Ride with confidence on the trails this summer! And be smart about where you ride.