Though there isn't much difference in the syllabus but you should consider checking the previous year question paper for the two states, there lies the difference. 

Also when it comes to results, CBSE often gets better results because leniency n checking and level of question paper.

All the best!!

dear student

First thing I would like to say you that there is not much difference in syllabus of any two board of education whether state board or national board for any stream and every board follows the syllabus prescribed by NCERT and hence there is no difference between the syllabus of Haryana board and CBSE for class 12th

 there can be a slight difference in question pattern of different boards but the syllabus remains the same as for higher studies every student must have gone through the same syllabus in their higher secondary degree to have better understanding.

hope this helps

All the best!!!