Northfur:
The current Canada Post module is terribly out of date. Canada Post has abandoned the Sell Online platform years ago, and uses only Rest/Soap. The solution I have mashed together, of the Shipping Boxes Manager module and Advanced Canada Post produces rates, but the box manager is terribly inaccurate with its logic for packing boxes, and the advanced Canada post module won't return rates for Tracked Packet, Priority and other services.
It's been 4 years since the Canada post Module has been updated, if twitchtoo or anyone can produce a module that works with CP's new platform, and handle boxes in a competent way, I'd gladly contribute money towards it.
I'm still using last Canada Post mod from the plugin page. Priority Shipping apparently doesn't work but I don't use it. I use the includes/modules/shipping/candapost file as written, not modified as mentioned a few posts back.
The boxes and packing work well for me and the quoted rate is usually dead on, or at least very close. It did take some fiddling years ago to get my box sizes set - its important to have length, width, depth in the same order for each box. And I created boxes that accommodate multiples of those dimensions and in the same sequence. (an item sized as 8x2x4 will NOT fit in a box 4x2x8 - instead the mod will search for the first box defined to accommodate the former. squence)
There was an issue, years back when I was on zc 1.3.7 - using the 'free shipping mod' resident in zen cart conflicted with the Canada Post Mod - the solution at the time (that I still use) is to leave the free shipping mod uninstalled and define free shipping threshold in the Canada Post set up (where the box sizes are defined).
My biggest gripe with Canada Post is that their site goes down more often than I like - affecting not just zen cart mod but other CanPost online services.
I am, however, looking forward to an update as it is surely a matter of time before it all goes south on me ;o)
Currently using zc 1.5.5f, php7.1