Sète-Tanger (2 nights on the boat), Tarifa-Tanger (40 minutes, after crossing Spain). There are several companies like Comanav or Comarit.
Fez airport is the nearest, 40 Km from Meknes. You can come to Meknes by taxi (about 40 dh), by train (35 dh) or rent a car. Several companies fly to Fes (Royal Air Maroc, Jet4you, Atlas Blue, Ryan Air...)
The train Elipsos comes from Paris to Madrid every day, then a train from Madrid to Algesiras (spain), then a boat to Tanger and finally a train to Meknes. This travel takes 48 hours from paris to Meknes.