Unless the bride is a professional singer, she should not be singing to the groom at the wedding.
Unless you are a professional, please don't sing at your own wedding. The emotions of the day may make singing difficult. The bride should thoughtfully spare her guests from listening to her struggle through the teary, emotional rendition of a love song . . . expressing emotions that should best be expressed privately, perhaps?
And usually if the bride is a professional singer, then she already knows what she wants to sing.
Good luck with your planning.