When I was younger and was up to all sorts, I spent a lot of my life crossing dover to calais by various means, I think we did the Hovercraft 3 times a day, so I remember exactly what is was like and the same there was a catamaran too.

But I like the look of this BF one, its been a long time since I got on one I just feel they must be better than the early 90's !

The old Seacat, just did a google images search, all coming back to me now !

We drove via Rouen in October last year and the main bridge in the city centre was closed for what looked like major repairs. It caused heavy traffic congestion and no little confusion as the sign posting is not that brilliant. You are ok if you have a Sat Nav, just get yourself to the other side of the river but ignore it until then as it keeps sending you back to the closed bridge.

The drive through Eastern France via Lyon and crossing at La Jonquera is both expensive and during the summer months, very busy. Also, your journey past Barcelona should be taken with great caution as the area is prone to thieves telling you about a non existent problem with your tyres. When you stop to examine, you are robbed. This is particularly so for foreign plated vehicles.

We have found the journey up to San Sebastian and crossing to Bordeaux the best by far. Cheaper and quicker and stopping in the Bordeaux region is a must for the wine if nothing else.

We use the tunnel as the sea legs in both of our families bypassed us!

On the Rouen/Le Mans/Bordeaux/San Sebastian route - the only city you would need to pass through is Rouen and this is surprisingly easy, well signposted and around the outskirts and not the actual centre. Top Tip - zoom in on Google Maps/Streetview and 'drive' the virtual route at the tricky bits so that the signs and directions are familiar when you get there and you are in the correct lane etc.
Also, if you decided to use the N1/A1 in Spain then Madrid is also surprisingly easy to traverse as most of the route is underground in tunnels which are also well signposted if you know the number of the road you want to get out on - which would be the A5.
PS - you can also get detailed turn-by-turn directions from Google maps, which includes signposting and tolls (and radar cameras!), by entering 'Calais to Chicliana' in the search box, then use the map view to 'drag' the route onto your preferred route if necessary.

[PPS I know that the OP has already travelled but I thought I would add this in case anybody else was thinking of using this route]