My opinion would be to keep everything in Laseriche.   For documents you create, scan and push to Laseriche, having Laseriche be the sole location makes sense.

For documents where Junxure creates a file in the "P drive", I would recommend that you establish an import agent job that monitors those folders and brings them into Laseriche.  With Workflow, you can have the appropriate metadata assigned and the document routed to the client "P drive" folder in Laseriche.   We mirror the Junxure folder structure in Laserfiche.

The documents we have found that are automatically created in The Junxure P drive are:  templates, document wizards, email attachments, and the batch report generator in PortfolioCenter.  

With Import Agent we ensure all documents are in Laserfiche.  Using the integration outlined in the other post, you can then interact with the Laserfiche documents through the Junxure application.

Result:  all documents are in Laserfiche and you can interact with them via Junxure for a seamless end user experience.