I hope he has insurance, and he needs to contact them straight away if he does. If he does not, he is out of luck, and $400 is a bargain.
It sounds like he has a back injury, the area has swollen and is compressing on a nerve. However, it is hard to estimate the degree of damage to that area, whether it is serious or not. It will obviously be up to him as to how he proceeds with this.
I would also go and get the police report and ask them how he can proceed with an insurance claim against the other driver in case this turns out worse than it is right now. He could also check with the person of the car he was in, and check with their insurance company as to how they could seek damages from the other driver. If you do not have insurance when you attend a hospital in canada, you will be charged, and really he is lucky he is not in the states, he'd be paying a lot more.
Good luck. It is only free to attend if you have a provincial medical card, and each province will look after any person in canada who has one. I would be very surprised if he was not advised to take out medical insurance when coming here.
This might be of some use. I asked a friend who lives in Canada.
Marion