Obviously it's super early and only the highest of level Cassie's will have a more concrete idea of her matchups, but just for funsies, here's what I think currently (subject to change of course). And I'm just gonna go with "wins, loses, or even" based off of initial impressions and personal experience in matches instead of numbers cause the game isn't old enough yet.
Also, I'm no high level player so... grain of salt and feel free to laugh at/blow me up for this.
Sonya - Even (her zoning is good, but cassie can go under it with hers. However I think sonya is stronger up close)
Baraka - Even (very similar to sonya)
Skarlet - Even
Sub-Zero - Even
Raiden - Wins (teleport could be a headache, but Raiden is trash tier up close)
Scorpion - Loses
Liu Kang - Even
Shao Kahn - Wins (get zoned lol)
Kano - Wins
D'Vorah - Wins
Kabal - Even
Jade - Loses (could be even, once you get in on jade, Cassie is better than her.)
Johnny - Wins
Cassie - Even (With the edge going to non valedictorian Cass
)
Erron - Loses (Eats her projectiles, full screen 50/50s, just as good up close, etc)
Jacqui - Wins
Kotal - Wins
Noob - Wins (outzones him, and makes his high projectile useless)
Jax - Wins (see gross vs tyrant, hard for jax to get in)
Kung Lao - Wins
Cetrion - Even (her zoning is better, but Cassie is better up close)
Kollector - Wins
Kitana - Wins
Frost - Wins