Originally Posted by
Symmetre
To be honest it really depends on where and when you're flying. On many routes the majority of pax check bags, so there's more overhead space than you might expect. On other routes it's just the opposite, and the gate agents are begging people to check their bags at the jetway. Most Westjet GAs and FAs are pretty accommodating, providing that space for the bag actually exists.
This has nothing to do with the original question, mind you, which was about the size limit of checked bag and not carry-on bags.
At Toronto where you toss your own bag into a machine there was nobody checking for size limits and I doubt the laser scanner can measure small variances in size per the original question. Weight it can and probably does.