Diploma

yes u can study. But as per my biew you should do it in india itself. Because I too was trying for abroad, I have scored 80% of marks in diploma final year electrical engineering. If you go to abroad for studying b.tech then there is not much difference for b.tech in abroad and india. While job same preferance is given. Rather than go abrod for studying M.S or M.B.A.

You may take up IT, networking and IT, business management etc. Take a look at following colleges and see what interests you more.
Some of the leading institutions in Canada, which offer a PG Diploma are:
Durham College
George Brown College
Sheridan College
Algonquin College
Humber College
Seneca College
Centennial College of Applied Arts & Technology
Confederation College of Applied Arts & Technology

Find here, the one from Bangalore is the best one.
https://www.shiksha.com/getListingDetail/87921/course/course-P-G-Diploma-In-Medical-Law-And-Ethics-Pgdmle-Bangalore-India

yes you can get admission in coep after diploma in direct second year but cutoff Is high

can I join after graduaction in.b.com.radiology.

Hi Mehtab, why do you want to do a diploma after BBA? You must look for PG Diploma or Graduate Certificates. Either ways, yes you can pursue a PG level course in Marketing if it suits your career plans. Seneca is a popular college and also offer co-op education which is very helpful for students.