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Here are some possible sources. Guaging public opinion is rather difficult back so far. There are no records of public opinion polls, and most people probably didn't write diaries that have survived for two thousand years.
http://www.google.com/search?sourceid=navclient&aq=&oq=roman+rupublic+vs.+&ie=UTF-8&rlz=1T4VRHB_enUS648US649&q=roman+republic+vs+empire+&gs_l=hp..0.0i22i30l5.0.0.2.295164...........0.Bm0_7oU182M