thanks for the info Andrew

So i haven't booked yet as there is no advantage for me to buy a latitude flight now that doesn't guarantee me a first class seat

i could end up flying tango plus and have the same chance of upgrading if we waited until 4 days before

the benefit that I would get (please let me know if this is right)
is if I bought latitude now and 2 upgraded seats are available for us (say in the next week - more than a month ahead of the departure) we would get upgraded if i used my eUpgrades since with latitude fares you can get upgraded before the 4 days before departure

Air Canada would have my money now if i could use my eUpgrades in combo with buying 2 latitude fares....