Migrate MySQL Master-Slave to Percona XtraDB Cluster

I’ve found some variations on the ways to migrate MySQL to XtraDB out there, but none of them seem to be what I’m trying to do. I have a current MySQL 5.5 master-slave configuration and a 3 node 5.7 XtraDB cluster for POC. Connectivity from the existing MySQL DB nodes to the POC XtraDB nodes isn’t an option. Of course trying to import a mysqldump failed with:

ERROR 1105 (HY000) at line 53: Percona-XtraDB-Cluster prohibits use of LOCK TABLE/FLUSH TABLE <table> WITH READ LOCK with pxc_strict_mode = ENFORCING

What options are there to migrate data from an existing MySQL setup to XtraDB if direct connectivity for replication isn’t an option?

You can change pxc_strict_mode to PERMISSIVE before loading the dump file, please be aware of the consequences if you change that variable though - https://www.percona.com/doc/percona-xtradb-cluster/5.7/features/pxc-strict-mode.html