The aquabus are these little ferries that hop back and forth across False Creek carrying people between the downtown core (visible in the image) and the rest of Vancouver to the south. There are three bridges that cross False Creek, but if you fancy a ride in one of these ferries, it's a stylish way to travel.
The rainbow is the symbol for diversity. And Vancouver has a very diverse population. Now I'm not talking about different nationalities or anything, this is all about sexual orientation. We have a huge community of gays, lesbians, trans, bi, and just about anything you can think of (and probably a few you can't). Much like the owner of this aquabus company feels like showing their pride, you can find rainbow flags all around the city, though you'll find most of them in the West End, which seems to have taken up the mantle of being the 'diverse' neighborhood. The rainbow adds a colourful splash when the world seems to have gone gray.