Justin here - just wanted to offer some insight into that for you.
I haven't used Leadpages personally, but I did find this page going over the topic.
It seems the best option would be to contact their support, but here is an excerpt from one of the Leadpages responses:
"While we do not officially integrate, if you sign up with a plan that allows full HTML export you can export the content of your LeadPage and publish it as a page template inside of Shopify.
From there you will have to adjust some of the CSS as Shopify may override some of thestyling from LeadPages.
Another option is to link from your Shopify site to the LeadPages hosted on our server. "
So, in essence, if you can export your HTML code from Leadpages, you can create a page in Shopify with that information, or simply link your shop into an image or a menu link. I have a reference guide on how to create an additional template within your theme as well.
That should do the trick!