Tony Montana: I always tell the truth. Even when I lie.
Tony Montana: In this country, you gotta make the money first. Then when you get the money, you get the power. Then when you get the power, then you get the women.
Tony Montana: I kill a communist for fun, but for a green card, I gonna carve him up real nice.
Tony Montana: All I have in this world is my balls and my word, and I don't break them for no one.
Tony Montana: [Wielding a grenade launcher.] Come and say hello to my little friend!
Tony Montana: Who put this thing together? Me, that's who! Who do I trust? Me!
Tony Montana: You know what? Fuck you! How about that?
Tony Montana: He's such a good lawyer that by tomorrow morning, you're going to be working in Alaska. So dress warm.
Tony Montana: Me, I want what's coming to me.
Manny Ribera: Well, what's coming to you?
Tony Montana: The world, Chico, and everything in it.
Tony Montana: Why don't you try sticking your head up your ass. See if it fits.
Answer: It's unlikely a set up. Tony is supplied with money and guns to defend himself. If this was a setup, the toad would've had more details. He would've known Tony had backup with guns and they would've waited to ambush them. Also makes no sense for Omar to put himself at risk without a legitimate opportunity to make cash. Frank knew about the deal as he supplied the buy money. Omar seemed loyal to Frank. Why would he send some low level thugs to be set up losing his boss' money in the process? All he would do is lose trust and be suspected.
Omar was an informant. He wasn't loyal to anyone. Omar's driver is the one that suggested to send Tony to the Colombians. And I think Omar knew the Colombians were shady, and that's why he sent Tony. It was, in a sense, a setup.