They are language-learning friends who started to interact in BOTO's Next Star.
Episodes Suggesting a Friendship
In Go, Battle Monster! Boat says they should become friends only to remember that he's French, so she tries to learn French. Baguette then tells her that she's got to read the subtitles.
In A Treasured Welcome, Boat carries her team down the mountain and Baguette says "Merci Bateau!"
In Downhill Disasters, he repeats "Bonjour, Bateau, comment ca va?" from Episode 4, when they race to the finish.
Episodes Suggesting a Conflict
In BOTO's Next Star, Baguette said "Bonjour, Bateau, comment ca va?" and Boat yelled him away.
They were competing in a tiebreaker in a fanon episode.