Istanbul plus Paris or Barcelona?

We were excited to pick Istanbul for our honeymoon but also want to add on a few days in another city and are stuck in between Paris and Barcelona. Both of us I’ve been to Paris during high school so I’ll very long time ago and only I have been to Barcelona. My fiancé really wants to see only the sagrada Familia in Barcelona but overall it feels like Paris would be much more of a honeymoon like add-on

For context we love exploring food drink and unique neighborhoods with lots of history. We love big cities but know the vibe of the people of Barcelona is much more up our alley. We know the food will be better in Paris but it doesn’t have the Sagrada. Also we have both been to Paris (only me to BCN) so have seen most major sites – so if we went it would be to see some sites and then mainly explore neighborhoods, take river cruise, eat great foods.

if we are going to have a similar experience however in Istanbul should we choose Barcelona to see the one and only sagrada instead? Do you think Istanbuls city experience will be too similar to Paris anyways given we have been before?