I have stayed in all three. The Delta and Marriott are literally a block apart. I first stayed at the Marriott on my honeymoon many, many years ago when the rotating rooftop restaurant still rotated. It was the first hotel I'd experienced with heated floors in the bathroom and was formerly a Holiday Inn - believe it or not. Most of my stays were for work and none left a great impression in more recent years. The Sheraton is probably best of the three for location if walking. Lounges are hit or miss at all, if open during your stay. As you have already ascertained, the Westin is the best Bonvoy option if the budget allows.
There are a couple of other posters here with solid local knowledge. I've only been once since Covid and stayed at the Westin. The Sheraton was undergoing renovations, although still may be an option if the lounge is open. Some reports suggest the Delta discontinued their lounge. Check these threads:
Sheraton Ottawa construction/restaurant closings?
Delta Ottawa - No Breakfast/Lounge
Originally Posted by
flyme2
The Ottawa Marriott Hotel[1] (formerly a Holiday Inn, then a Radisson Hotel) is a hotel located in Ottawa, Ontario, Canada, on the north-west corner of the intersection of Queen Street and Kent Street. It was built by Campeau Corporation as part of the second phase of the Place de Ville complex. Upon its construction in 1971, it was the tallest building in Ottawa, but the title was short-lived when the neighboring Tower C was completed in 1972. As of 2013 it was the sixth tallest in Ottawa and eighth in the National Capital Region.
The Radisson then moved a few blocks over to 402 Queen St. and has since disappeared from the Ottawa market. Coincidentally, that property is now a Holiday Inn.