Yes, you may reserve cambio vehicles in all cities and regions. Using your cambio card, you may use cambio cars in all of Belgium and even in the German cambio cities. Your tariff plan is valid in all of Belgium, in Germany the German Aktiv tariff applies.
Have a look on the website of cambio Germany to see where they are based.
Do you have a MoBib card instead? It is also valid in all of Belgium. Unfortunately, these cards cannot be used to pick up a car in Germany.