At most locations, it is not possible (at least not online) to reserve a specific model.
Gosh, even when you reserve a specific car class, you often get a different class (hopefully higher) when you arrive.
The models listed on the website are typically just examples, and if you read the fine print you'll see so. Exceptions might be expensive premium cars, but I doubt an Escalade falls into that category.
And car rental companies often don't know their car mix well in advance (are they going to buy a whole new cars between now and when your rental occurs?), but near in they don't which exact cards are going to be returned on time. So now matter how far out, they might not know what exact cars will be on the lot at the hour you arrive.