Dear Andrew,
Thank you for submitting the question here. Unfortunately, we don't have a tool to migrate the data from j2store into EShop.
However, I will find a way to export the data from j2store into excel file and use EShop Import Pro tool to import the data into EShop. I think it is possible to implement. Please go to our ticket system
joomdonation.com/support-tickets.html
to submit a new ticket to EShop category to send me more information so I can find a custom solution for you.
Sincerely, Giang