Yes, it’s possible to pursue a Ph.D. from a foreign university after an MTech from IIT Guwahati or IIT Hyderabad. However, you have to choose your MTech guide very carefully as the recommendations of professors are very necessary for Ph.D. from a foreign university. Many professors have excellent connections in universities abroad and these recommendations are highly useful to make your career smooth.
In order to determine which professors have such backgrounds and connections, contact the students who have already done their MTech under them.