Most sunflowers are heliotropic - meaning they follow the direction of the sun, as it moves across the sky - however some of them that lose this ability when their blooms reach maturity becoming too heavy for the motor cells to control the movement. Typically though you'll notice that their leaves will still tend exhibit this behavior throughout their life cycle.

IIRC, most vining and wild sunflowers are not heliotropes and tend to be fixated in an easterly orientation. If you know the specific cultivar of sunflowers you're considering it might be easier to lookup.

Randomly, most non-dwarf french & africian cultivars of marigolds are also heliotropes and will have blooms that track the sun throughout the sky.

Mine followed the sun all the way through maturity, until the blooms dried up at the end of the summer last year. It really tickled my daughter to watch the transition. :-)