Will I be prone to identity theft if i don't cancel unused credit cards?

ID theft is an issue with every credit card which you need to protect. However, if you cancel this credit card, it might affect your credit score, lowering it a bit. It may affect your credit utilization ratio since the available credit limit will decrease. Moreover, it might also affect the length of your credit history if it's one of your oldest cards.
So, it can be a better idea to keep checking your credit card statements and credit reports to avoid being a victim of identity theft.

Instead of cancelling the credit card, manage it properly. Pay attention to the statements to avoid any fraudulent activity.

How many unused credit cards do you have? If you have only one unused credit card, then you can cancel it. That won't affect your credit score much. Just make sure you pay off the outstanding balance before closing the credit card. It will help to boost your credit score. And, if you want to cancel several unused credit cards, then cancel them one by one. That won't increase your credit utilization ratio.

You should take care of your credit cards even if you are not using them frequently. Your old credit card account may effect your credit score, so make sure you should use them when required.
Keep an eye on the credit report and your credit card statements. If you find any error of unusual activity, contact the credit card companies.