Along with licensing comes liability insurance, first aid certification, training courses, ect. I'd feel a lot more comfortable with a guide that was insured and knew what had to be done if I happened to go for a swim un-expectantly. Guides in BC are licensed, they all have to apply for the waters they want to guide on each year(not sure if there is a limit to how many guides can be on a certain river or not), all must complete certification, and must be insured.
Heres a thread on another board in regards to guiding in BC. http://www.flybc.ca/forum/index.php?showtopic=7267
Colin