I have gone through your project spec. I have few question to clarify project scope.
Questions:
Please let me know in which 2 sites do you want to compare?
Will you provide the APIs of those 2 sites?
Which data after comparing do you want to show at your site?
Please feel free to contact me through Message Board, I will be happy to reply you back. Please write more about your project requirements. I’ll try my best solutions to address you as soon as possible.
Regards,
Malabika