Not sure - can't think of anything that they would have in common. I reckon they wouldn't be close but still get on with each other :)

Merida and Belle could be like sisters, one mature and one immature, both learning more and expanding their horizons.

It would be a weird yet close relationship

Lets send Disney a movie request in which all the DP meet.

I doubt it.

Best friends don't have to be 100% alike, and they both want adventure

I know opposites attract sometimes but I don't really see these two bonding. I don't think they'd hate each other though, just have a mutual respect for each other but never actually converse.

Leaning towards no. While I don't think Belle believes in obeying parents unconditionally( I think she definetely doesn't) and think she definetely would approve Merida's desire to escape arranged marriage and she wouldn't be a fan of Elinor's parenting style. But I DO think Belle would find Merida's methods of rebelling rather dirty, far more dirtier than Jasmine or Ariel's whose actions endangered themselves and not their parents( well, in Jasmine's case but Ariel's actions at least meant to endanger only herself, Ariel didn't ask Triton to sacrifice himself).