Yes, you can! Some US pet insurers imply in their marketing pitches that other pet insurers restrict yur choice of veterinarian but at the moment, all pet insurers allow you to choose any vet you want to go to in the US.
Now, there are two discount programs that are not insurance programs, which restrict you to their network of vets (see menu on the left for "non-insurance options") but as I said, they are not insurance providers, just discount programs.
