In the Kekkon e no Michi series (結婚への道シリーズ), also called the "On the Way to a Wedding" series:

1. Irekawatta Hanayome (入れ替わった花嫁; A Bride in Waiting):
   THE SUBSTITUTE BRIDE
   Dr. Lucas Daniels viewed his bride-to-be's temporary disappearance with exasperation, fondness and resignation. After all, she felt the same way about him! Then a beautiful stranger strolled into town, looking exactly like his fiancee. In order to avoid upsetting their families, Lucas asked Sara Martin to stand in as the missing bride. But now he was wondering which bride to marry....

Sara had been searching for a family, and now her wishes had come true. Not only did she have wonderful parents, but the look of love in her pretend groom's eyes warmed her heart. But when the clock struck twelve, would it end her fairy-tale dream or give her a true happily ever after?

2. Hanayome no Okurimono (花嫁の贈り物; A Gift for the Groom):
   BORROWED BRIDE

Dark and devastating RI. Nick Claiborne's love 'em and leave 'em policy was suddenly in jeopardy. Because his new client, Analise Brewster, not only insisted on "helping" him uncover the mystery of her fiance's past, her irrepressible spirit tempted Nick to forget his vows to stay single--and hers to wed another ....

Spending time with a lively, loving woman usually made Nick want to run-but this time he found himself taking Analise with him. Yet once they'd found Analise's gift for her groom, would Nick be the one walking down the aisle?
(info from fictiondb)