There are many differences. Here are a few: Master's is more expensive and requires much higher marks and higher IELTS scores. Master's is much more difficult as a student. A Master's is a university degree (a diploma isn't).
Scholarships are typically given to those with high marks. So I would say it's unlikely you'll get a scholarship without good grades. You'll have to contact the school you are planning on attending to find out what marks are required to obtain a scholarship.