In the remake, Hauser infiltrated the Resistance but fell for Melina for real. He was caught and had his memory wiped by Cohaagen in the hopes of eventually getting him to return to the Resistance and unwittingly lead Cohaagen to Matthias.

It simplifies the story, but Cohaagen has no way to track Quaid, since Quaid removed his tracking device, and there's no Benny to keep tabs on him. Cohaagen magically finds and assaults the place with no prior warning from Matthias' guards or anything.

What would have been kind of awesome, in retrospect, is if Lori had managed to switch places with Melina during the Wonkavator sequence using the disguise device, and Quaid (having been told by Melina where to go if they got separated) actually brought HER to the Resistance in a pretend-injured state. Then Lori-as-Melina could suddenly perk up and murder Matthias and take cover, and THEN Cohaagen could start the assault.