Yes, "Google" is a search engine. We can see "Google and Bing are search engines. ("Google" can also be short for Google, Inc., a corporation whose first and most famous product is Google, the search engine). However, Google isn't primarily an online bookstore. Are you sure you are not thinking of Amazon? There are many different ways to express your idea. One way would be: "Unlike a brick-and-mortar bookstore, an online bookstore has no space restrictions, and can display hundreds of thousands of books."