With that kind of dispairity in price I would get a third opinion...but in the end it won't really matter. These are just quotes, once they really get started pulling wire and making changes then you will know the real cost...which is usually less then the most expensive guy but more then the cheapest.

Not sure about Canada...but you also want to make sure they are certified and bonded to do the work (they should also be card carrying union members...another saftey measure for you). You electrical work is one think you don't want to skimp on...to much fire risk.

Hope this helps and good luck,
Sean