You can't always know where a game is going to go. Run a game long enoug (frequently just one or two sessions with some players) and your PCs will grab the narrative and take it in a direction of their own. It's a natural part of running games, and something you can't really prepare for. Sometimes though, you plan these crossroad moments yourself, and then as the session comes up, all you can do is hope you pull it off right so the players make the choice they want.
You Need Momentum
One of the key things, in my experience, to a proper crossroads moment is momentum. The game needs to be moving under its own weight. By that I mean that the players are invested in their characters, and the characters are making decisions that - perhaps - the player doesn't agree with or aren't the most tactically optimal choice to make. You want these things because it lets the story moment be more enjoyable. Sure, you always want your players to choose the path that is most fun for everyone, but if that decision comes from the "character" more than the player, then that is just damn fun.
The Choice May Need To Be Marked
Your players are capable of grabbing the wheel and jerking it to the left on you at almost any moment. However, in this post we're talking about when you plan a crossroads moment, and while the PCs can always just to go wherever, you need to make it a bit more clear. You don't want players going past this moment and not realizing that they could've gone a different way that was all planned out for them. Make it noticable. If you can, put a small pause - only a small one, we don't want to break the momentum - and make it clear, than start things back up and see where the players go.
Be Prepared For An Unplanned Avenue
So you have your crossroads planned, you show it to the players, and they just go smoothly down the new path or continue forward, right? Well, maybe if you're ridiculously lucky. Be prepared for your players to see a choice moment and justr go off in their own way. Often this will be the way you have the least planned. You figure they can go left, right, up, or forward? They'll bust out shovels and start digging. It's just how things go sometimes, so be ready for it.
Ultimately, It's Not Something You Force
Under no circumstances should you try to force a choice to be a big deal for the players. Make it clear that they have the choice, but don't try to force them to hem and haw and debate it. It's ok if they're already set and just want to plow forward. It's ok if they're having fun just jerking the wheel in random directions. If it becomes a thing? Great! Go with it. Just don't force it. It kills it for everyone.