My son got 149 in IIT JEE mains, 92 % in CBSE 12-th exam and likely to get 78 in JEE advance. What are the possibilities for him. He prefers integrated M. Sc in Physics. Can you advice us?

I am assuming that you are from General category.
As your JEE Advance marks are very less, you will not be able to clear the cutoff. Hence, you will not get M. Sc in Physics in IIT Kanpur. So, you may be able to get this branch in any other college but it would not be so good as it is in IITs.
Thanks