Whenever I've flown the minimum price on the bid wasn't worth it (in my opinion at least). Although they've been all fairly short haul domestic flights (ie Halifax to Toronto).
Reading the FlyerTalk thread on BidUpgrades the consensus seems to be that Last Minute Upgrades are cheaper.
https://www.flyertalk.com/forum/air-...early-bid.html
http://www.flyertalk.com/forum/air-c...ir-canada.html
http://www.flyertalk.com/forum/air-c...-upgrades.html
http://www.flyertalk.com/forum/air-c...ades-here.html
http://www.flyertalk.com/forum/air-c...questions.html
You could also look to see what the fare difference is between the upgrade and the ticket you paid. If it's the same or cheaper call up Air Canada and get them to upgrade your ticket. From what I understand this is done at no charge, only the fare difference as you're giving them more money.