I have always been under the impression that, no matter where you are or where you go, any public space or business establishment cannot refuse entry to a guide dog. Store, restaurants, office buildings, public transportation.
Now I think pets are a different matter, and I'd personally check with a cab company or even a public transit operator (train, bus, etc) to check on a pet policy. But a service animal, no way they should be refused. And I don't think you should have to ask in advance either. They serve a purpose and a function.
You should not have to ask for a service animal. Wheelchair accomodation sure, you need a different and very specific vehicle for that. But not for a service animal.