This is not only for Marriott hotels but several Marriott hotels are participating. Buy 3 nights, get 3rd night free. The 3rd night is rebated upon check out. Or go to the specific Marriott hotel, under "Deals & Packages" tab, and look for "3rd Night Free, buy 2 nights get 3rd free"

Of course this rate can be higher, so you'll need to calculate to see if it comes out better.
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Stay a third night on us in Ottawa!

Spend more time in Ottawa for less this summer—your third night is on us! Reserve your getaway at participating hotels between June 1 and October 10, 2022 to take advantage of this special offer. It’s the perfect time to get inspired in Canada’s capital! For more information regarding this promotion, please see the terms and conditions.

Bonus: When you take advantage of the 3rd night on us offer, you automatically qualify for our Double down on fun promotion which includes credits to dine and play at the Rideau Carleton Casino – Future Hard Rock! Plus, if you’re an Ontario resident, you can save even more with the Ontario Staycation Tax Credit.

• Must book a minimum of three consecutive nights at an Ottawa hotel through the Ottawa Tourism website
• Offer valid for new bookings made during promotion dates (June 1—October 10, 2022) and for arrivals between June 1 and October 2022. Limited time offer
• Rates and conditions may vary and are set by and at the discretion of the participating hotel