Migrate Planner to Project?

As has been stated there is no integration out of the box, and it would be difficult to do completely because not all of the fields in Planner map to Project anyway; specifically for scheduling Project needs start/finish dates which could relate to Start and Due date in Planner.   Planner has no concept of dependencies either, so again this would be "problematic" to say the least.  I think the best option would be just to export the planner plan to Excel, and then copy and paste the task names into Project, along with the start date if you have it.  If you are using resources, these will need to be split out (but see my blog here on how to do this in Power BI - the same theory applies to Excel https://applepark.co.uk/powerbi-planner-template/ ) .   

Basically, there is going to be a lot of manual work required to take a planner plan (effectively a nice task list) and craft it into a meaningful resource loaded and levelled schedule.