I know la unified is 1-5 elementary, 6-8 middle, 9-12 high school
I’m curious if northern California is just different (I did grade 1 and 2 in LA)
No, its the same.
The schools closest to my house in the burbs of LA were k-6, 7-8, and 9-12. I’m not even sure if that was standardized within the district though. 
So why are school districts in California called “unified” and school districts in Texas called “independent”?
They’re not all ‘unified’ in California. LA unified is called that because, well, it unified several districts, and serves multiple cities.
I remember school districts in and around LA called unified but I don’t remember what they are called in San Francisco because I don’t know any school aged kids in that area. But all over Texas they’re all called “Independent school districts”.
Same reasoning applies. A lot of the school districts around LA used to be be separate districts for k-8 and high school and / or were formed from districts from multiple cities.
edit: looked it up, and so many school districts in TX are called independent because they’re that - they’re entities independent of municipalities or counties, and have independent taxing authority separate from that of other gov’t entities.
Does Canada have 3 year Uni Degrees and/or Diploma with fewer people doing a year 13 (or A level)? New Zealand Degrees are mostly 3 years but they have Year 13 (in most cases).
Im not sure, i left canada in high school. Most of my friends/family did 4 year. I think only ontario has grade 13, not sure . In BC the norm is 1~12