The 10th-ranked Jabeur, the only top-10 player left in the women's draw, had lost five of her six matches against Alexandrova from 2016 to 2018. The Tunisian is the first Arab player to reach a WTA 1000 final.
It will be her sixth career final and first since a runner-up finish in Charleston last month.
"This match is going to be different [from the Charleston final]," Jabeur said. "I'm just going to really give my best. I don't want to regret, saying like, 'should I have done this, should I have done that.'"
Pegula and Jabeur are tied 2-2 in head-to-head meetings.
The Associated Press contributed to this report.