Dave is right. Although the instructor will expect you to have a reasonable grasp of the FAA regulations - he will not expect you to have an encyclopedic knowledge of the FAR / AIM
Remember that a BFR is conducted with an instructor, not an examiner and is a REVIEW rather than a test, although of course if the instructor doesn't think you're safe - he obviously won't sign your log book.
There are lots of differences between flying here and in the US - principally with the classification of and rules relating to airspace. Having flown a lot both here and in the US, I would say that this is the thing most likely to trip you up. Also, being foreign will cut little ice with the FAA as an excuse if you bust some Class B airspace.
You might find this book handy . . .
http://www.flyaas.com/acatalog/Onlin...GUIDES_45.html
It's basically the questions (and answers!) that an FAA examiner might ask an FAA PPL candidate prior to his / her flight test. I very much doubt that an instructor would expect you know know much more than what's in this book for a BFR.
Finally, if you've not already sent your paperwork (and money!) off to the CAA - do it in plenty of time. The FAA won't issue your licence until the CAA have contacted them to confirm that you're a real person
