GNSS receiver looks like MediaTek MT3333 with external amplifier+filter+chip antenna. And ARM7 CPU.

The watch has at least 3 Cortex-M4 microcontrollers, not counting Ant+ or GNSS chips! Microchip ATSAMG51, ATSAMG53 and MAX32360

nRF51422 contains ANT+ and Bluetooth LE functionality. And Cortex-M0 CPU to run these.