To go to Vancouver, I have to transfer in Shanghai. Can I go to a hotel to rest in Shanghai?

Yes If the connecting flight needs to stay overnight, the airline is not responsible for arranging accommodation. Most connecting flights take less than 24 hours. Most airlines don't provide accommodation unless the flight is delayed overnight. If you can go to a hotel to rest, you can consider a nearby hotel. The price of staying in a hotel is not very high. Generally, there will be one near the airport, or you can find a hotel nearby.