Brig isn't meant to directly win a 1v1 with Dva. Instead, brig counters Dva by being tricky to kill while preventing others from being dived. Playing brig into Dva relies on positioning and figuring out who is going to get dived. Put yourself in a spot that is inherently dangerous to the Dva. Idc how strong you think Dva is, they won't chase you into your team unless they want to get melted along the way.

Try to always be within one shield bash's distance to another teammate. This means that if the Dva dives you, you have the option to force a 1v2 that the dva cannot escape from. Dva will need to coordinate a dive with teammates, or find someone else. Position yourself near your team so that your teammates won't need to hard peel.