I just contacted Autoeurope and they told me that when booking through their site, I would have to pay the tire management fee at pickup, in addition to their listed price.
Suddenly, the huge price gap between autoeurope's site and avis.ca (pay now rate) was filled with this extra fee... :-(
So I ended up just booking directly at avis.ca - but did a sign-up for Hyatt's gold pass thing, and saved 11% when entering the code :-)