CYYT (St Johns) to CYQX (Gander) is approx 3.5 to 4 hrs by road depending on the weather. Both acceptable and most accomodating for all aircraft types. Ref 9-11
CYHZ (Halifax) is also an excellent diversion airport.
CYFC(Fredericton) is usable; however have a look at the runway lengths, instrument approaches and hours of operation.
Hope you never find out!!
Jeeper