Depending on the company you are renting from you may not require a boating license (Pleasure Craft Operator Card) to rent a houseboat. Often a completed boat rental safety checklist is sufficient for the duration of the rental. You will need to keep this checklist/document readily available if requested by officials.
Based on personal experience to ensure you enjoy your vacation with confidence it is recommended to obtain your Pleasure Craft Operator Card which is available online.
For more details check out the Transport Canada website on this subject and operating any pleasure craft: Pleasure Craft Licence
A list of questions and answers are available: Pleasure Craft Operator Card - FAQ's
For a list where to get your Pleasure Craft Operator Card: List of Accredited Course Providers
Be sure to always check the Transport Canada website for all the latest requirements. Being aware of the requirements are your responsibility.