Samsung has generally offered its flagships in two flavors: Snapdragon in North America, Latin America, and China, and Exynos for the rest of the world. The Note 10 could see a paradigm shift, as word on the grapevine claims all Note 10 models, bar the Verizon ones, will be powered by an Exynos SoC, likely the Exynos 9825.
https://www.notebookcheck.net/Samsung-is-being-touted-to-almost-completely-revert-to-Exynos-SoCs-on-the-Galaxy-Note-10-phones.428586.0.html
I would be (happily) surprised if Samsung doesn't lock down its Exynos bootloaders for U.S. carriers. I can't see AT&T in particular selling a major phone with an unlockable bootloader.