Yes, you can do Bcom(H) after completing class 12 in Science Stream but definitely you will have to face disadvantage of marks in calculation of best of 4 , if you take admission in Delhi University. Also for applying in other colleges as well, you will have to face the disadvantage as preference of Commerce students is there.
Anyways, as far easy or hard is concerned , it would be difficult for you to understand the concepts and terms because study of B.com(h) includes mostly what all commerce students have studied in class 11 and class 12 like related to Business ,Accountancy and Economics. Everything will be new for you as study of science is entirely different from commerce. Lots of time is needed to analyse and understand the cases of relevant concepts.
It won’t be hard but at the same time difficulties might come that can make it hard especially for non-commerce students.