J Lo arrived in style at Friday's big debut for her and Ben's movie, "Unstoppable," which is showing at the Toronto International Film Festival ... and she's showing lots of skin in a bejeweled dress.

Ben co-produced the movie alongside his BFF, Matt Damon -- it tells the true story of wrestler Anthony Robles, who was born with one leg and overcame major hurdles on his way to becoming an NCAA Division I champion at Arizona State University.

Jennifer has a starring role as the wrestler's mother ... and the film is already generating Oscar buzz.

The premiere comes a little over two weeks after Jen filed to divorce Ben -- who's not in Toronto for the film's premiere BTW. He was spotted out in L.A. Friday ... where photogs caught him flashing one of the biggest grins we've seen from the guy.

Our sources say Ben's in the middle of post-production for "The Accountant 2" and spending time with his kids this weekend ... hence not running off to TIFF for the flick's premiere.

TMZ broke the story ... because the estranged couple has no prenup, everything they acquired over their roughly 2-year marriage is community property, which means the assets acquired during the marriage are divided equally ... including Ben's production company, Artists Equity (AE), which produced "Unstoppable."

In other words, J Lo would be financially entitled to a share of the profits generated by AE's recent and upcoming hit movies, including "Air," "The Instigators," "Small Things Like These," "The Accountant 2" and, of course, "Unstoppable."

Our sources told us last month Ben and Jen have been trying to hash out a settlement for a while now ... but the negotiations haven't gained traction and now they aren't even speaking on speaking terms.