Would you be able to transfer to a UC with a software engineering major?
No UC’s offer SE as a major other than UCI so you need to transfer for CS at the other UC’s.
What is your CSU GPA?
Yes, you can transfer as long as you have all transfer requirements met by Spring prior to transfer if applying for Fall.
This link shows UC Transfer GPA admit ranges by major and campus.
https://www.universityofcalifornia.edu/infocenter/transfers-major
Around what GPA will I need to be competitive for transfer?
Depends upon your target schools. Look at the link for the GPA admit ranges.