More risk-taking and defiant vs. less risk-taking and reminding Merida more of Elinor.

Agree with wavesurf, I think Tia would be too mature for Mer.

^

Ariel knows hot to have more fun and actually lets herself have fun. Tiana needs to be convinced to have fun before she gets into it. Merida would prefer someone who just naturally enjoys it.

She's all about rebellion against a parent and being in control of her own fate, so it seems likely she's more prone to relating to Ariel. Tiana is a little too meek for Merida.

She would relate to her as both are rebellious, except her decision for sold her voice for Eric, she can't stand it as she don't care with romance things.

Definitely. I think she'd really connect with Ariel.

most definitely. wanting to live a different life than charted out for them, feeling trapped in their current role, rebellious, risk-takers, explorers, fascination/curiosity with new things. Taking shortcuts for their goals, reckless, wanting to be independent but needing loads of help from others.
Tia is very mature, practical, low-risk taker, prioritizes work over fun, denies having fun coz she has to work. Merida isn't much interested in serious work and is centered on having fun