Film where two couples exchange their partners

Should be from around 90’s or early 00’s woman in invited to her ex husband’s wedding where she meets man sitting at the piano (if I’m not wrong) and turns out that the man is ex husband of protagonist’s new wife. They start going out. I don’t remember much more but there are some things I vaguely recollect:
1) Two teenager kids (one from each family are also involved). In one scene they’re watching TV or listening to music together. They oppose to craziness happening in their families.
2) Woman owns big dog that sleeps on bed
3) She participates in cake contests with ugly green cake.
4) She is blonde and might look like either Madonna, Sharon stone, or maybe Michelle Pfeiffer
5) In the end they return to their old partners.