You can say, for example: - Will you be free to help me? - Will you be available to attend our meeting? Saying "can you be available to help me?" though I think it is not grammatically incorrect, it does not sound natural, so I would suggest going with one of the other options. As an additional note, using "would", if you intend to ask for a favor, is also very polite and respectful: "Would you help me with my homework?" "Would you open the door for me?" Regards, Jaime :)

If you are talking about the future, you can say, for example 'Will you be free to come to the meeting tomorrow?' or 'Will you be able to come to the meeting tomorrow?' They don't mean exactly the same, but both will work.