Among the GMC vehicles that the Arcadia replaces are the Safari van and the Envoy SUV. It is the first unibody vehicle from GMC and also the first front wheel drive passenger vehicle from the GM division that has been around for decades.
Without a doubt, the Acadia is intended to be an entry level vehicle into the crossover SUV market. It has a V6 engine making a robust 275 horsepower and a technically advanced 6T75 6 speed automatic transmission that promises faster acceleration and better fuel economy than similar current GM vehicles.
Like with the Yukon SUV, GMC is expected to release an enhanced Denali version of the Acadia. That car will likely have a V8 engine and improved luxury interior, among other trim changes.
These cars are still new, so don't expect them to pop up on used car lots any time soon. You might be able to find a few dealers selling excess on eBay for discounted prices. You'd be surprised how many dealerships do this.