Buses from Kanazawa to Shirakawago

I would like to take a bus from Kanazawa to Shirakawago. Is taking the bus operated by Nohi Bus in the link below the only way to travel from Kanazawa to Shirakawago by bus?

http://www.nouhibus.co.jp/english/shirakawago_kanazawa.html

It says that reservation must be made to take the bus from Kanazawa to Shirakawago which operates only twice a day. Is the reservation can only be made by phone call? Is there any website that I can make a reservation?

Thanks.

Is taking the bus operated by Nohi Bus in the link below the only way to travel from Kanazawa to Shirakawago by bus?

It is by far the fastest, cheapest and easiest way to get from Kanazawa to Shirakawago by public transportation. You could theoretically make huge detours via Takaoka or Takayama, but it would not make any sense.

It says that reservation must be made to take the bus from Kanazawa to Shirakawago which operates only twice a day.

It is three times per day. Unless you travel on a busy day, there is no need to make advance reservations, and you can just buy the ticket at the bus terminal on the day of travel.

Is the reservation can only be made by phone call? Is there any website that I can make a reservation?

Online reservations are possible in Japanese here:
http://www.j-bus.co.jp/web/asp/hnsent5.asp?mode=1&id=21&id2=19