Another missing thing for Halifax is a bridge over the Northwest Arm. This has been contemplated for about 100 years but never built. The Northwest Arm is only a couple km from downtown, is 5 km long, and only about 200 m across.
A drawing from a 1945 plan:
Source
The aquatic gardens were never built either. The rotary by the end of the arm is there and so are stretches of Connaught and Chebucto Road in 1940's-era boulevard form. But Connaught abruptly ends somewhere in the middle of a residential area without connecting up to anything in particular.
This project was also supposed to happen in the 1970's and connect up with a highway through downtown and third harbour bridge that were never built. That is probably for the best but the Northwest Arm bridge by itself would be useful.