Bus service to downtown Ottawa from Merrickville is offered by Howard Bus Service - Route 509:

Route 509 - Merrickville - Ottawa  (via Burrit's Rapids, Kemptville, North Gower)

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Bus service to downtown Ottawa from Kemptville is offered by Kemptville Transportation Services - Routes 542 and 543:

Route 542 - Kemptville Express- Ottawa - Gatineau 

Route 543 - Kemptville - North Gower - Ottawa