I really would like to see it in Toronto, Canada, besides being in my home country and favorite city, it would lead to a refreshing change of tone. In the US, all the factions are decided, as well as the environment. The whole this is static and done. Doing it in Canada would allow for new factions, and thus, new themes to be explored. Furthermore, because we were only technically a part of the US, we wouldn't have been much of a target. A lot of the infrastructure would still be standing. There would be radically different monsters running around, who evolved to suit the unique environments even more.
However, if I were to pick a location, I might also pick Salt Lake City Utah. Fact is, the mormons that live their have become a powerful force comparable to the old Templar. Imagine what we could do with that, though it would be controversial, it is interesting exploring the idea of what Christianity and this particular branch, could become over time when stressed to its limits. Throw in some fear of technology and ultra conservationism, and you've got an interesting lens to explore the limits of faith and humanity.
That said, I really hope Bethesda just stays out of fallout's way, and leaves it to the pros at Obsidian who actually know what they're doing.