Both models are rated IPX4 for sweat and water resistance. You can’t use them for water sports or wear them in the shower, but either pair will be safe from damage at the gym or in the rain.
Of course, the AirPods Pro are going to be best for sports with a tighter fit. The AirPods 3 will surely be better than the 2nd-gen model though.
Both the AirPods 3 and AirPods Pro offer spatial audio for immersive listening and adaptive EQ that tunes sound based on how the buds fit in your ears.
Apple boasts a new custom driver and a high dynamic range amplifier in the AirPods 3. We won’t know how these two models compare sound-wise until we try them, but both pairs run on Apple’s H1 chip.