At the time of the last Falkland conflict, the US was busy sternly disapproving of the UK flexing its military muscles on any continent that had "America' in it, and Canada was way too peacable to provide support for any military actions by NATO allies that might involve (gasp) gunplay. Now the US has come to rely on the UK as its best and greatest ally, and Canada has remembered that allies are expected to fight for each other.
Should a second conflict begin, Canadian and American ships would flank the deployed British battlegroup, and US AWAC and tanker assets, and the use of US bases would allow the British to utilize its Tornado groups very aggressively. Likewise I would expect both Canadian and US fighters to make a big show of establishing "No Fly Zones" to keep all but the most suicidal Argentine fighters restricted to their own continental airspace.
To make a strike for the Falklands when you do not know if the UK is willing to shed blood for a sheep covered rock on the back end of nowhere, and you are reasonably certain her allies will not offer any material support, is a reasonable gamble. That was then. To seek to attack the Falklands knowing that the UK will pay in blood and treasure to take it back, in the sure and certain knowledge that her allies will fall all over themselves to demonstrate they are standing shoulder to shoulder with their British allies in their time of need, and knowing that the troops that the UK will send are now battle tested on land, sea and air, is political and national suicide. This is now.
The Argentines may rattle sabers, and even shout at the UN and OAS, but the sabers will remain most carefully in their sheaths.