see ref.

voyage de détente / voyage pour le plaisir
the difference is slim I think !!!

une proposition

I would hesitate to propose a term for either in FR, but I think I may be able to help explain the difference being expressed in EN.

As far as I understand it, 'leisure travel' refers to travel in connection with some existing leisure activity — for example, a skiing / golfing trip, a diving / surfing holiday, etc., or possibly to be engaged in some cultural activity, like a painting course or a music cruise.

'Pleasure travel', on the other hand, is just travelling for the fun of travelling — going on holiday

In some ways, the former may be regarded by certain travellers almost as seriously as business travel — for example, you might well be more furious if your delayed flight made you miss the World Cup Final than if you simply lost a day on the beach!

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Note added at 8 hrs (2007-09-08 08:17:59 GMT)
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I see from the footnote to your question that 'voyages d'agrément' has been accepted for 'leisure', which would not be consistent with my suggested interpretation above.

If that is the way your client is distinguishing the terms, then I think they must mean 'leisure' = things like going on holiday, where the actual journey is only a means to an end; and 'pleasure', where it is the journey itself that is the purpose (like a coach outing or a river trip) — in that case, Dominique's suggestion may well be closer than I at first thought!

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Note added at 11 hrs (2007-09-08 11:12:12 GMT)
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(I was, of course, referring to Dominique's earlier answer, now hidden)

Le terme ‘voyage’ est certainement mal adapté, car trop restrictif.