Canada

you need minimum 60% marks. you also need IELTS. 6 band

Being a dentist unless you register in that dental council registration you can not do immigration. first step is your registration. then you can process your immigration

What you want to study is entirely your choice, ideally a course in accounts, finance, international business would be good which is what you are planning. There are a number of courses again related to finance or accounts such as financial planning, applied finance etc. Plan your career and choose what to study.

Yes you can apply for pc diploma in these countries with M.com however the requirement differ from country to country and college to college. like for Canada and Australia IELTS is mandate where as in Newzeland exception can be granted.

what is your current qualification

you can apply for pathway programs that's leads to university degree program . It can be a preparatory course or an ESL program

Than these universities Germany is good to study and also cost of living comparing to others

Only after obtaining a proper license from the province in which you plan to work. You will get all the details here.
http://physiciansapply.ca/practising-in-canada/

Hi
Gap years are problems only in India. If you can explain the reason for it, there would not be any problem. so choose universities and apply