ok, here's what happened.

My wife flew back from Portugal on Transat.
She showed the 12 day old positive test result; no recovery certificate, just the PCR test result; no problem.
She declared a positive test more than 11 days old in Arrivecan.
Got to YYZ T3; Nexus line.
No one asked to see any Covid docs, including Arrivecan.
Got the green sticker on the passport walked out of the terminal with no test requirement, no quarantine requirement or any other document checks.

I flew back from Amsterdam on KLM.
Exactly the same as my wife's experience, except I could upload my vaccination/ positive test/ recovery certificate (recovery certificate not required, but I had it, so I uploaded it anyway) to KLM in advance. Even though the KLM page says residents of Canada cannot use this service(?), I still got a 'validation' email stating: 'We’d like to let you know that all your COVID-19 related documents are approved.'

Thanks everyone for replying to my original query!

P.S. : rebooking notes:

both airlines rebooked us on flights a week later with no fees or fare difference charges.

KLM's Amsterdam number was very hard to reach, just delivering a message that the 'wait time exceeds 45 minutes, so we will hang up now' - and then actually hanging up! Eventually I got through after 30 minutes when I tried phoning on Sunday at 3 a.m.

Transat has a number in the app (didn't see it on the webpage) specifically for pax already at their destination who need to make changes. It worked well, 20 minute hold during regular business hours. And they seamlessly transferred our 'dog in hold' reservation as well. I didn't expect to be giving Transat the highest marks, but I am.