Hi Laèrcio, I hope you are well and that you are doing something fun this weekend. If you are asking about specific plans for Saturday and Sunday and today is Monday, Tuesday, Wednesday, Thursday or Friday, say: "What are your plans for the weekend?" or "What are you doing this weekend?" If you are asking about what someone regularly does on the weekend, say: "On the weekends, I spend time with my friends." or "What do you do on the weekends?" I hope that is helpful.

"What are your plans for the weekend?" This is the correct sentence. It's not possible to use "which" or "to" here.