Is it significantly harder to apply as a CS major rather than a Business at SDSU
No, both are competitive majors since the whole campus is impacted. Select the major you want to pursue at the time of application. You are admitted as a Pre-major so you need to complete the screening courses with a required GPA before continuing with your major courses and officially declaring the major.
For Business, you need to complete the screening courses with a 2.0 GPA and a SDSU cumulative GPA of 2.9
For CS, you need to complete the screening courses with 2.0 GPA and a SDSU cumulative GPA of 2.0.
as a freshman, a 3.7 and 1300 will probably get you into either…
You may want to ask each department to verify that it will not change degree requirements without sufficient prior notice or allowing students partway through the requirements to complete the old requirements, as the SDSU EE department apparently did, causing some students to be unable to graduate on time: http://talk.qa.collegeconfidential.com/college-life/2074999-my-school-made-horrible-changes.html