There's not enough information to be able to tell how you should market it!
You should get hold of a copy of the Writers and Artists Yearbook. This lists all of the agents in the UK and contains loads of advice. Basically, look for a agent who deals with work in a similar field to yours, check their submission guidelines and take if from there.
As for whether you should go UK or Oz, that would depend on which territory you think you would sell most copies in - given the populations of each, the UK's likely to be the best bet. Foriegn rights are always worth much less than domestic rights.