Google’s latest update to Google Maps will add wheelchair accessibility data. A note on whether any given place is wheelchair accessible will show up on its page when you view it inside the app.
Unfortunately, this service is a bit incomplete right now, as Google is relying on user inputted data. As such, for locations that don’t have any data you’ll still probably want to call and see whether they can accommodate you.
It’s also worth noting that this is only available in the US right now. There’s Google for ya’.