Probably no, although there will apparently be some minor new dialogue about Geralt's mark in the DLC with Ciri, Triss, and Yennefer (2-3 lines with each), most likely available during the Final Preparations quest (level ~28-30). The expansion quest line itself is designed to be playable at any time, but it is recommended for level 30 and above, that is why I guess it is ideally done in act 3 of the main quest after returning to Novigrad from the Bald Mountain.
I may (and would like to) be wrong about main characters not being present in the expansion pack, but integrating it into the open world design with the possibility of playing the expansion quests at any time makes adding them fairly difficult for the developers; see
this post for an example why. It would be easier with an expansion that is either a separate smaller game (with something like "New Game - Blood and Wine" added to the main menu), or one that can only be played after the main quest is completed. For similar reasons, I do not think the expansion quests will have any significant consequences on the main game.
Another thing that suggests that none of the main characters will be in the DLC is that they are not present in any trailers, screenshots, or other marketing material.