Huddersfield v Catalans final would be interesting.

To quote spegs , no it wouldn't

Warrington or Wigan vs Catalans would be a great game (assuming that Catalans had Todd Carney, David Taylor, Glenn Stewart, Anthony Gigot and Eloi Pelissier would be playing), and the event would probably sell out all but the members sections. I would expect 88,000 - 90,000 attending such a spectacular game.

The last final to get over 80k was Saints vs Hull FC (82k) in 2008

Since then we have had finals such as Leeds v Wigan, Leeds v Warrington, Wigan v Hull and all have fallen bellow the 80k mark.

Any game featuring Catalan would do well to hit 65-70k and that is being ultra optimistic.

Leeds v Hull KR 80,140

I stand corrected.

Actually, to be factual the 2010 final between Leeds and Warrington drew the biggest crowd at the new wembley of 85,217. That will take some beating and won't be beaten by any game involving Catalan imo.

If Catalan bring more than 5000 fans I'd be very surprised and I think I'm been generous with that number

Indeed.
If the final was in France, e same would apply to any English clubs fans travelling over there.
There would be plenty of neutrals supporting them, especially if it was against Wigan or Leeds (oops).

But it will be the French residents of London, plus all the neutrals, who will be excited by the contest -- especially after they get a glimpse of David Taylor, Todd Carney, Anthony Gigot and Eloi Pelissier in action.