These are great questions and I'll try and answer all your questions as systematically as possible. Both scholarships and university applications depend upon your overall profile. Factors such as your Statement of Purpose, Letters of recommendation, Certifications, Social work, etc. along with your scores, play a major role in your application.
Being an 'undecided major' allows you to enter your chosen college without declaring a major and thus, allows you to explore your interests. Your SOP is what sets your profile apart from the other applicants'. Therefore, it's a highly important aspect.
Since the IELTS exam is more widely accepted, you can definitely try taking it. However, it still largely depends upon the country you choose.
In order to make an exact analysis, we'd need your exam scores and other details. But depending upon the program and university you choose, as long as you have a solid profile overall you can definitely get into top universities. If you need help choosing the right program/university based on your scores and preferences, you can always contact us or register with us. Hope the answer helped!