The danger of winter ferries is ice. Even if the river does not freeze, there is ice coming from Lake Champlain, often without warning. It is dangerous for a ferry to go aground, especially when vehicles are on board.
Some projects exist, but it is complicated. This is considered marine transportation, so managing such a service is quite difficult.
In terms of the bridge, the infrastructure is there. All it takes is the will of the government to complete the project. It could be a great tripartite project to which the municipalities and regions, the provincial government and the federal government would contribute.