If you're looking for a meeting place or a good stop around ½ or halfway between Rochester, United Kingdom and Canteleu, you can try Outreau, France, which is about 2 hours southeast of Rochester, United Kingdom, or about 2 hours north of Canteleu.
Another possible place to stop near the midpoint is Berck.
About ¼ or a fourth of the way, you can stop at Dover, United Kingdom. This is almost an hour southeast of Rochester, United Kingdom.
About ⅓ or a third of the way, you can stop at Calais, France. This is a little over 1 hour southeast of Rochester, United Kingdom.
If you drive straight through without stopping at all, the total distance is 339 km. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 3 hours, 58 minutes.