I don't think if that's right to compare Arsenal and Juventus and say if Sporting will have a harder game against Juventus than Arsenal or not. It is not the same story for Juventus I think Juventus will try to avoid making the same mistakes as Arsenal in order to avoid giving Sporting a chance to win the game because both teams will use different systems. Arsenal lost the game because Sporting knew their weaknesses and how to overcome them. While Juventus will try not to do the same mistake as Arsenal in order to give Sporting a chance to win the game.
Juventus will look forward to playing defensively, Alegre often does this, and Arsenal tried to solve everything in attack. I'm not sure if Juventus are stronger than Arsenal, rather the opposite, but you're right that the teams will have different strategies and that will determine the outcome. It is very difficult for me to determine a favorite for myself in this confrontation, the teams have equal chances, probably Juventus is more sympathetic to me, but this in no way means that they are stronger than Sporting.
After beating Arsenal now Sporting is good contender for the title because this was good game and with this win things completely change in this event Juventus is also good side right now even after losing 15 points they are doing good job in Serie A which is surely impressive with this most chances home advantage could be vital in this round for the both teams because if Juventus will be able to have better home result in first leg then surely things could be not easy for the Sporting with Juventus is mostly love to play defensively and this is working for them with too many clean sheets already under their belt but Sporting which is currently at their best will also try their best for the another exciting win and place into next round.