Whilst we cannot really advise on how to integrate with InfusionSoft, we can advise on what is most common practice.
Integrating InfusionSoft Autoresponder With Squeeze Pages
Integrating InfusionSoft Members & Payment Systems
We do not have advanced knowledge of how to integrate with InfusionSoft beyond using the autoresponder coding. What many of our members do is use the InfusionWP plugin (http://www.infusionwp.com/) which allows you to link InfusionSoft to your WordPress site - and you can use this to secure your membership pages built with OptimizePress so that your InfusionSoft products can be delivered inside your OptimizePress/Wordpress members area
As far as we are aware, InfusionSoft does not have a natural integration with WordPress so this is the most popular method of integrating the two based on feedback from our members. For more assistance with integrating these two please either check the InfusionWP support or hire a web developer to assist with the integration