By default, Siri does web searches using Bing. So, if you say, "Search for iPhone cases" it will show you results from Bing's search engine. You can also request that Siri use a specific search engine and it will launch Safari to that search.
How to search the web with Siri
- Press and hold the Home button or say "Hey, Siri" on your iPhone or iPad to activate Siri.
- Say something like "Search for iPad cases" or for a specific search engine, "Search Google for iPad cases."
Siri will automatically launch Safari and search for what you requested in the search engine you requested.
That's all there is to it. If you just ask Siri to search the web, it'll use whatever web browser you have set as your default in Settings, which you can also change anytime you'd like. Give it a try and let me know how web search and Siri work for you!