We did a reverse image search and found that the picture of the couple is photoshopped. As per a report by News 18, the original picture of the celebrity couple Deepika Padukone and Ranveer Singh was clicked when they posed for photos on their visit to Siddhivinayak Temple, in Mumbai on November 30, 2018. Here is the actual picture:
Other pictures from that trip prove that they wore the same dress as in the viral picture.
No, Ranveer Singh and Deepika Padukone haven't campaigned for BJP. The viral picture of the couple is photoshopped in which a texts "Vote For BJP" and "Vote of BJP N Modi" have been digitally added.