Group E - #5 Brazil, Great Britain (England is #9), #23 New Zealand, Cameroon NR
Group F - #3 Japan, #4 Sweden, #7 Canada, South Africa NR
Group G - #1 USA, #6 France, #8 North Korea, Colombia NR
Ranking are FIFA. The tournament is like this
Assuming USA/Japan/Brazil all win their groups, USA and Brazil get marginally easier quarterfinal matches against third place finishers, but then USA and Brazil would play one another in the semifinals.
With that said, Japan has a tougher group. Assuming Japan wins is a bad assumption, they could easily come in second. In fact, assuming anyone wins a specific group is bad. Japan came in third in their group at the 08 olympics. USA came in second to sweden in their 2011 WC group. Japan came in second in their group at the 2011 WC.
Brazil seems to have the easiest group by far, NZ and Cameroon should offer very little resistance imo. Japan's group seems the toughest.
Japan does not really have the easiest road to the finals.