By the Maritime Link project (HVDC), which finished this year, Newfoundland is linked asynchronously to Nova Scotia, which is part of the Eastern Interconnection.
No, the Quebec's grid is isolated from the rest of the North American continent. This is due to the historical decision to make sure that Quebec is 100% independent in terms of energy production. This also mean that Quebec is capable of rebuilding its network in case of a total black-out because Hydro-Quebec regulate the voltage of its grid and the frequency.
The only interconnection between Newfoundland and Labrador and Quebec is the DC interconnection for Churchills Falls dam.