If buddie goes canon, I really need it to be Eddie who makes the first move/confession. Its the most satisfying conclusion to their arcs and is most fitting for their characters.
Buck has spent his whole life being left behind or being someone's second choice. Maddie left him, Abby left him, Ali left him, Tommy, Bobby etc. His parents only had him to save their son, and when that didn't work he had to do EVERYTHING to get their attention. Abby left and never told him she was coming back, instead getting engaged to someone else. Tommy really actually wanted Eddie, not Buck, and instead settled for Buck when it was clear it wouldnt happen with Eddie. Even the dog left. Its also true that, at least in his eyes, he is never the most important person in the lives of those who are most important to him. He is Bobby and Athena's son, but they both have their own children, same with Maddie, who raised him. He's Chris's dad, but he has Eddie, and will always have Shannon with him. And then theres Eddie.
Eddie who got his girlfriend pregnant in high school and felt he had to get married to her, Eddie who felt he had to be with Ana because Chris liked her and it was what was expected of him, Eddie, whos abuela tried to set him up on dates that he hated because he felt like he had to perform, Eddie who lost Marisol amd Chris because he couldnt let go of Shannon due to his lack of closure and control surrounding her death - sudden, painful, and right after she said she wanted to break up. Eddie, who's parents controlled every aspect of his life to the point that he no longer felt joy for the things he loved, leaving him riddled with religious guilt and taking away his one constant (his son).
That all leads to Eddie finally being able to make a choice for himself, choosing joy - choosing Buck. And Buck finally being chosen, being put first and having a concrete, indisputable place in a family of his own.