Rollers will be a better option than using a brush as it has a better converge and other benefits. That's because if you use a brush to apply water-based polyurethane, it's going to leave brush marks. On the other hand, the roller helps to eliminate those marks. And also, you'll get a better range to work with, which will make the whole process a lot easier and faster as well. That's why you should go for a roller as it's a far better option than a brush. Yet, you can use a brush for that as well if you want to. Just make sure that you use the best brush that you can get, and the bristles are very soft for the application.