Bismillah,

Asalamu Alakyom, Please refer to the following answer:

https://www.al-islam.org/ask/is-it-sinful-for-a-girl-to-marry-without-the-permission-of-her-parents 

Also it is not recommended for you to marry a person from the sect who refers to itself as Ahlus Sunnah unless you can make him Shia. It could also be haram if it would cause you misguidance too. It is better to marry a spouse who will raise any potential children on the love of Ahlul Bayt (peace be upon them) and disassociation of their enemies. I have met many people of both mixed Shia-Sunni parents and in most cases, the children take after the father in the Sunni way or become confused. 

In this case, your parents could be rejecting the person for the above reasons. And when you say 'you like' such a person, you must ask yourself what this is based on? Is it due to over stepping the Islamic boundaries such as how he looks, or is it due to his religion? If it is for the wrong reasons, then one should not pursue such a marriage especially if it may be based more off lust or wordly reasons. 

May Allah grant you success