Just catching up this morning, I attended the public session last night and had a good chat with the folks there.
They've posted this on Shape Your City -
https://shapeyourcitysaintjohn.ca/harbour-passage-extension
On the right side of the page, in the document section, you can download the boards to view them more clearly. There were some additional diagrams at the event showing detailed changes to the roads, but they don't appear to be included.
Having the path on the east side of the street, prior to Union, is great to see. Based on the diagrams, it will use some of the vacant land and require a slight narrowing of the street. They will have several 'feature plazas' along this stretch, too, overlooking the water.
They said they didn't want to take the path under the causeway by the rail tracks, as it would be kind of dark/sheltered/unsafe, and they would prefer it to be more open and visible.
North of Union will be a dramatic change. Except near the intersection, they are suggesting reducing the lanes from 5 to 3 (1 northbound, 1 southbound, and a turn lane). I am not personally against this, but the rabid anti-bike lane crowd on Facebook might be.
For the Crown St overpass, they are suggesting changing from 4 lanes to 3. The two northbound lanes would remain unchanged, but one of the southbound lanes would be lost. Changing the bridge in this way would require structural modifications because the loads differ from those originally designed for. I am not an engineer, but that does not sound like a straightforward task. When I asked them about working with the province on that, they initially laughed.