They would probably be different. Obviously, there are enormous variations within both British and American English, so you can't generalise too much. Within the UK alone, there are dozens of different ways that a native speaker might pronounce a word. However, the most typical British pronunciation would probably sound like 'wontid', whereas a typical US pronunciation would probably sound closer to 'wan'id'.

It's really hard to say. Both British English and American English have many different dialects with many variations of vowel pronunciation. I guess the standard might be that American English speakers might pronounce it "wantid" and a BE speaker might pronounce it "wanted".

An American English speaker would be more likely to omit the t in fast speech. http://www.forvo.com/word/wanted/#en The pronunciation from Singapore sounds very much like Br.E and the one from the Philippines sounds like Am.E.