- China sent aircraft carriers to the North (way the hell north) Pacific or into the Arctic.
- China somehow based planes in Russia (although they would still have to cross Alaska to get to Canada if the maps are correct).
- Canada sent their F-35s to the Pacific to confront the Chinese in, say, Korea.
For (2), please. Yes, there might be some Chinese/Russian alliance down the road, but again, the threat would be more Russian than Chinese. And there would never be enough F-35s to offset the Russian planes, so a few Chinese ones added is not a big deal.
For (3), yes, the previously purchased planes did engage in alliance operations, including most recently over Libya. The problem with the Pacific, besides being pretty vast, is that Canada does not have the same kind of institutional ties/commitments. There is no NATO out there. Perhaps one could interpret the legacy of the Korean War (suspended by cease-fire and not settled) as a commitment by the Canadians to defend South Korea. But when was the last time anyone in Canada discussed seriously Canada's commitment to the defence of South Korea? Oh yeah, that is an ... American problem and a Japanese problem. The RCAF is not going to be called upon in a crisis to deter a North Korean invasion. Plus we are back to talking about North Korea and not China.
The combo of Arctic and China as the threat to Canada is just incredibly silly. Yes, China could develop bombers with sufficient range to hit Canadian targets, but it is not clear why one would need stealth fighters to thwart that threat.
No, there are good arguments to make about the F-35, but they are not about China. And mostly not about the Arctic. What unifies the folks who have been interested in the F-35 (Denmark, Netherlands, Australia, Japan, Norway, etc) are desires to be interoperable and save money via economies of scale. Well, the latter has pretty much dropped out due to escalating costs. So, the real reason (besides perhaps some local industries making some money--not that they could not make some money some other way) is the desire to be able stay with the US and other allies in a fight. To be able to fly the first day and not just the third day after the US knocked out the other's side's defences. To justify the F-35, then, requires taking seriously and committing quite deeply to the future of multilateral military operations especially with the US. Otherwise, somewhat less special planes could be bought to deal with the more ordinary threats of hijacked planes, smugglers and whatever else.
I used to be agnostic about the F-35 because I do see a role for Canada and other allies in NATO operations in the future. However, money does matter (when people say it does not or should not, they are ignoring the realities of tradeoffs), which means one must prioritize. The F-35 is incredibly expensive, which means it WILL crowd out other spending, whether that means less subs, less helos, less training and readiness or less something else we do not yet know. But less of something else is most certain. I would like to have Canada to have the best air force, but I am not sure that the F-35 would get Canada any closer to that goal of "best."