Hanasaku Wedding

Hana was working at her family's struggling flower shop when a boy came up to her and asked her to pretend to be his fiancee! Turns out he's the son of a rich family whose promised fiancee had ran away at the last minute. So he wants Hana to stand-in for her at the ceremony. If Hana would do it, he'll help pay off her family's debts!

(Source: Shogakukan, translated)