When we finish our "Best of Scandinavia in 14 Days" tour we will need to get from Bergen to Stockholm. Would it be better by plane or train?
Flying is usually cheaper and doesn't take 15 hours, which trains do, including a two-hour layover in Oslo. Try www.skyscanner.com.
I've flown from Bergen to Stockholm - SAS. This was mid july 2017 - my flight was very inexpensive, but I booked it months in advance. The Bergen airport is nice. Buses, light rail or taxi from downtown Bergen to the airport, which is southwest of city center.
There's also a high speed train between Oslo and Stockholm, which about 5 1/2 hours.
Unless you wanted to stop off and see places on the way, I'd definitely fly. To find all your options, use Skyscanner: https://www.skyscanner.com/