On this page of the Assassin's Creed Valhalla Siege of Paris guide, you will find information about the romances in this DLC.
Toka - romance
You will meet Toka at the very beginning of the DLC. In the Strangers Bearing Gifts mission. Unfortunately, you can't romance Toka. No decisions affect the relationship between her and the main character.
Pierre - romance
You will meet Pierre at the very beginning of the DLC. In the Strangers Bearing Gifts mission. Romance is only possible during the main mission - "Skal". You do not need to develop a relationship with Pierre by completing his tasks (Vive La Resistance), it is not required.
Talk to the man during the "Skal" quest - this is required to continue the storyline.
After the cheese throwing challenge, you will get romance options (the ones marked with a heart). You must select this option twice to start romancing the man.