Luger, now 36, scored 24 Premiership tries during two spells at the Stoop before heading out to France to play for Perpignan and Toulon.
And having experienced rugby life on both sides of the Channel, he is backing Quins to be celebrating at the Cardiff City Stadium on Friday night.
"I don't see why Quins can't win it," the World Cup winner told skysports.com.
"It will be a massive game for both sides as their seasons are relying on it, so it should be a fantastic encounter.
"Stade have been struggling this season and from the reports that I've heard they could be cutting back and having a bit of a clearout in the summer so some of them will be playing for their jobs and futures.
"I think there is more for the sides to play for in the tournament this year than in the past. This is their one chance of glory and the pressure will be on."
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