Hi
Both questions are not completely related. Technically it is possible to have different hosts for different folders - so it's possible to have yourdomain.com/fr/mypage hosted in France & yourdomain.com/en/mypage in the US (see also http://stackoverflow.com/questions/1848605/can-a-website-subdirectory-be-served-by-a-different-web-server)
If you have to choose between folders / subdomains - go for folders (see also this post: http://moz.com/community/q/moz-s-official-stance-on-subdomain-vs-subfolder-does-it-need-updating)
If you check the signals Google is using to determine which country you are targeting (check https://support.google.com/webmasters/answer/182192#2)
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1: geotargeting - it's perfectly possible to activate two webmastertool accounts for yoursite.com/fr targeting the French market & yoursite.com/us targeting the US market
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2. server location - is used as a hint & became less important with the use of CDN's (mainly important for performance reasons). If you use a CDN there should be no problem even when the "main" site is hosted in France.
-3. other hints like address, use of local language: it's probably a good idea to use the content-language metatag in the head of your HTML. If identical pages exist in different language versions - it's probably a good idea to use the hreflang tag to make it obvious to Google which part of the site is targeting which audience. For hreflang - this generator can be useful: https://moz.com/blog/using-the-correct-hreflang-tag-a-new-generator-tool & this tool to check if everything is implemented as should http://flang.dejanseo.com.au/
In your case - I would go to
- separate folder - geotargeted in Webmastertools
- hosted in US - if this not possible: use CDN
- if different language versions of the same page exist across the site: hreflang to make it obvious for Google which part of the site is targeting which language / country - use content-language metatag.
Hope this helps
Dirk