I believe they use the former First Choice B 767s with 258 seats and the CAA stats suggest that the passenger load is not limited to less than this.
Continental's Boeing 757-200s operated for five and half years between BRS and EWR, admittedly configured for 175 seats which I believe was their standard for this type of operation, and so far as I know the outbound flights never had to call in somewhere en route for a fuel stop.
As for Exeter and Toronto there seems to be no aircraft operating into EXT this summer from/to Canada - the airport's own website doesn't show Canada or Toronto as a destination either.
Canadian Affair will sell seats between Exeter and Toronto (I did a dummy booking on their website), either via Glasgow or Manchester. However, they seem to utilise Flybe on the EXT-MAN/GLA sectors.