I had been thinking about what if Bradley Walsh had come over to host The Chase (I think I remember hearing he did a pilot) and it got me to thinking about how often had a host of a show in the UK came across the pond to host its US import.
Off the top of my head, the most memorable example to me was Anne Robinson doing Weakest Link. Then, I remembered Jimmy Carr coming over to do Distraction for Comedy Central. Also, Alex Horne coming over to co-present the American version of Taskmaster with Reggie Watts.
On the flip side, globally, I recall Steve Harvey's recent foray into two different versions of Feud in Africa for both Ghana and South Africa. And, while not a US export, Howie Mandel helming Deal or No Deal to his homeland, Canada, while still hosting the American version.
I feel like I'm missing examples (couldn't think of an American host in the UK), but I also feel like this could be a very limited category of people.
Honorable mentions to Eamonn Andrews and Larry Emdur who hosted the versions of the shows that were exported to their home countries (although Larry was only a segment).