There is much environmental/mission logic in Canada having a nuclear propelled attack submarine (SSN) capability. Canada has much experience with land based reactors having being involved in reactor design since 1942 and currently having 19 nuclear power/electricity reactors. Canada's 4 conventional subs can only slowly traverse Canada’s vast coastline and oceanic distances (eg. all the way in the North Atlantic to Canada’s UK/Euro NATO allies). Canada’s future subs would ideally need to operate under ice for weeks - something only nuclear subs can do and/or do safely.
Russian SSN and SSBN’s traversing in/near Canadian waters are a potential threat that can most effectively be countered with SSNs. Also Canadian subs actually do missions far south to monitor Latin American drug smuggling – an operation coordinated by the US.
Against Canadian SSNs are cost, environmental concerns, US preferring to have the Western Hemisphere's SSN monopoly, US pressure that Canada’s naval mix compliments the USN, and that any confrontation with Russian or Chinese SSN/SSBNs may be high intensity warfare best left to nuclear weapons powers.
Also French, UK and US SSNs do temporarily dock at Dartmouth/Halifax Nova Scotia, Canada.
Canada has considered SSNs at least twice in the last 62 years. In March 1958 the Royal Canadian Navy (RCN) began reviewing the possibility of acquiring SSNs with some in the RCN advocating five US built Skipjack class SSNs in June 1959. The US was not enthusiastic especially when the RCN and Cabinet began to think in unaffordable, grandiose terms, a purchase of 12 US SSNs. Sanity prevailed when the RCN settled in 1960 for just 3 conventional Oberon class subs from the UK commissioned in 1965-68 (although 6 or 8 may have formed a more viable force). Three Oberons probably cost about 1/36th the cost of 12 SSNs. Australia also chose the tried, tested and successful Oberon class (six of them).
In 1987 Canada revisited the SSN question. But Canada again was wildly ambitious in talking up to 12 SSNs when even France settled for just 6 Rubis class SSNs for the French Navy. After only 3 Oberons buying 12 Canadian "Canada-class" SSNs would huge jump for Canada's submarine service (where surface ships are also required). The US would have been concerned about a major shift in the North American balance of power, especially if Canada chose French SSNs.
Canada’s Oberons soldiered on until the end of the 1990s after extensive upgrades when they were replaced by the four British Upholder-class. The Upholders, renamed Victoria class in RCN service, were not the bargain the UK advertised and suffered much internal rust problems, electrical problems, fire and other defects. Many of these problems stemmed from the UK RN "mothballing" the 4 subs for years in salt water.
Possibly the Upholders have been an even more off-putting public/political PR problem than Australia’s Collins. For many Canadians I suspect the Victoria experience has put them off the very idea of future submarines (replacements some time in the 2030, maybe).
Now in 2021 if Australian money becomes attractive enough (and US negative pressure on France not too great) then France might be persuaded to work with Australia first on six Barracuda class SSNs (entering service 2029-2035) replacing Australia’s Collins. If Australia’s take-up is satisfactory then Canada might conceivably buy six Barracuda’s (2036-2042).
More detail:
The Barracudas are smaller hence cheaper, smaller crew, and use only low proliferation LEU in their K15 reactors. This is compared to the much larger, expensive large crew, US and UK SSNs that literally have weapons grade (around 95% U235) HEU in their reactors. UK/US reactors being a definite high proliferation legal/PR problem.
So for construction and language training Australian workers/technicians/engineers and managers would all need to be part of the first Australian Barracuda SSN built in Cherbourg, France. Then the final five built in Adelaide. The work cost would be the same as the 12 Attack class would have been. The difference is that one SSN has twice the capability at 5 times the fully submerged quiet speed as an SSK. An SSK needs to run its loud diesels about every 2 days (which the Chinese would love to hear).
and
If Canada were to buy 6 Barracudas the first built (and less language training, bilingual Canada...) of a Can-Barracuda would be in France. Then five or more built in Canada.
Refueling of Aus and Can Barracuda’s might be possible every 10 years in Canada given established Canada’s nuclear industrial base. This may well be easier than Aus SSNs going all the way to France. It would also help cross-subsidise "economies of scale" in Canada's SSN costs.
Australia would very likely stick with the US Combat System (weapons, sensors (eg. sonars), some workstations/databases) used on the Collins and being designed for the Attack class. The common US-Aus combat system is a major benefit of the US alliance. The US also being Canada's major strategic ally...