Getting sick and tired of Montreal, would like to spend a day biking in Ottawa.
Any recommendations where to park the car near a bike bath for a 30 to 40 kms loop?
Near the Aviation Museum or somewhere near Parliament Hill?

I've lived in Ottawa way way too long and need to get out as often as I can; I cycle a lot in and around Montréal (just did ile Perrot and West Island yesterday, and Oka last week)

Parking near Parliament hill downtown can be fairly complicated and costly. I would personally recommend parking near the Aviation museum. At the museum itself, it is pay parking (around $3/h), but there are a lot of side streets nearby in the Manor park neighbourhood (St Laurent and Hemlock) where you could easily park for free on residential streets (some may be time limited).

Many nice cycling rides from there depending on your interests. For ex., along the Ottawa river to Champlain bridge, across to Québec and back along north shore and back by the Alexandra bridge. Many other options as well.

For this year or next year:

https://ncc-ccn.gc.ca/places/weekend-bikedays

Thanks. Will keep both suggestion in mind.