Can you draw a card from a replacement effect like Sylvan Library before you draw your normal draw for the turn?

Sylvan Library uses a replacement effect (CR 614.1) that modifies the draw step, not a triggered ability that fires before it. Specifically, Sylvan Library's ability says: at the beginning of your draw step, you may draw two additional cards. If you do, at the end of the draw step you must either put two cards back or pay 4 life per card kept beyond the first. The draws all happen during your draw step, not before it.

Your normal draw step draw (CR 504.1) is itself a turn-based action that happens at the start of the draw step. Sylvan Library gives you the option to draw two more cards in addition to that normal draw. All three draws occur in sequence during the draw step — none of them happen before your normal draw for the turn.

It is worth clarifying: Sylvan Library does not replace your normal draw. It supplements it. You still draw your one card for the turn normally (CR 504.1), and then separately you may choose to draw two additional cards under Sylvan Library's effect. The library resolves at the beginning of the draw step as a triggered ability that gives you options, not a replacement that fires earlier than the step itself.

Concrete example: It's your draw step. Sylvan Library's ability triggers and resolves. You choose to draw two extra cards, then draw your normal card for the turn — all three draws happen within the draw step. At end of draw step, you pay 4 life to keep the two extra cards, or put them back on top of your library. At no point do any of these draws happen before your draw step.

CR references: 504.1 governs the draw step turn-based action; 614.1 defines replacement effects; Sylvan Library creates a triggered ability at the beginning of the draw step, not a replacement of the draw step itself.