Are Newfoundland's and Quebec's power grid synchronized
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.