For Canada!
For Canada to get the Trafalgar Class I think we need a greater Soviet threat in the North Atlantic and possibly in the Arctic as well. If Soviet submarines start appearing off Baffin Island, playing the seagoing version of a Bear bomber encroaching on our airspace the need might be there.
The biggest problem though really isn't need in Canada, it's the politicians. No one politician or party is willing to hang their hat on an expenditure like this. Hell they fought an election over the purchase of ASW and SAR helicopters, 4 nuc boats would be epic.