Most every dash radio is installed into a single DIN (Deutsches Institut für Normung) or double DIN opening. Single DIN is 50mm high, 180mm wide, (2-1/8” by 7-1/8”) Double DIN is 100mm high (4-1/4"), 180mm wide. Some GM vehicles use 1.5 DIN, but adaptor plates to mound a single DIN in that opening, or a Single DIN in a Double DIN space.
The sky is the limit as far as features and models, don't feel constrained by what you have at present. Much better audio can be found at better price than a manufacturer's rebranded unit. Most audio shop/installers can sell adaptor plugs to match a new unit to the old plug or wiring harness. All the wires are usually logically color labeled, so wiring shouldn't be a challenge.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI