"if you want" is correct now. We may use them in the same situations, but there is a slight difference of meaning. You can want something even if you don't like it and you can like something even though you still might not want it. "quer" means "want" "gosta de" means "like" However, when asking someone "Would you like....." is used more often than "Do you want..." We want to do more than fill someone's need; we want to make that person happy. It is also more polite to say "May I have...." instead of "I want...", because the first is asking permission to have something rather than just stating a need.
For example, "I want a drink." but "I would like a lemonade." and "May I have a sandwich?" offers the host a chance to say yes or no.
There are two different contexts to this clause.
quer = present, indicative - Se você quer, eu também quero (If you want, I want it too.) The first sentence is a statement, I know what you want, now. ( ex. – Você diz que pode cruzar a fronteira. Se você pode, eu também posso. = You say you can cross the border: If you can, I can too.) There is no doubt what we are going to do.
quiser = subjunctive, future - Se você quiser, eu também vou querer. (If you want, I will too.) - The first sentence is an assumption, I do not know yet your intention, your possibility in the future. (ex. - Você diz que quer cruzar a fronteira. Se você puder, vou atrás de você = You say you want to cross the border. If you can, I’ll go after you. ) there is a doubt here.
a. Mãe, o João está pondo fogo na casa. Se ele
põe, eu também ponho. = Mom, João is setting the house on fire. If he does, I do too.
b. Mãe, o João quer pôr fogo na casa. Se ele
puser, eu também vou pôr. = Mm, João wants to set the house on fire. If he does, I'll get more gas.