Before we are born, do we pick who our parents, guides, and rebbaim in life will be?
Before a person is born, Hashem decides his or her basic life circumstances: whether they will be poor or rich, strong or weak, etc. The only thing that's not decided, and is up to the person themselves, is whether they will be righteous or not (Niddah 16b).
"Who one's parents are," then, clearly falls into the category of things that Hashem determines in advance.
"Who one's guides, etc., are" may be more of a gray area. Suppose that Hashem decides that one person should be born into an Ashkenazic family in America, and another into a Sephardic family in Israel. It is indeed more likely that each of them will have different teachers and halachic authorities, but it's not carved in stone; each of them may consciously choose a different path in Jewish life than what they were born into (or even, G-d forbid, abandon Judaism altogether).