Canada

I can't tell you much about diplomas as I am a B.Tech myself. But the main difference between a post graduate Diploma and an advanced Diploma is that a post graduate Diploma as the name suggests is a PG Diploma, whereas advance Diploma is same as the regular Diploma only that its a 3- year degree course as compared to a 2-year regular diploma. Masters as well as PGD, both are beneficial after graduation in mechanical engineering. But the difference between a Postgraduate Certificate, a Postgraduate Diploma and a Masters M.A. Or M.Sc. Or MS) is in the amount of credits the course contains. A general Masters degree contains a greater number of credits (usually 1.5 times) than a post graduate Diploma. More number of credits enables one to achieve better results with increased probability of scoring. So, it would be a wise decision to earn more number of credits and increase job and career prospects in a 2- year time which is same for both Masters and PGD. That's all I know. Hope it helps.

Yes, it is definitely possible but It might not be easy, you may not get the admission in top colleges/universities, However, there are some top ranked colleges/universities which won't consider your profile. Generally most schools require an overall band of 6 with not less than 6 in each individual section and the academic requirement is 65% - 75%, and this is not for all the universities and for you, work experience is an added advantage, my suggestion is to chose the course and university and consult the concern university admission officer and enquire about your eligibility. Of course the best way to be sure is to check each their websites individually.