Canyons tend to go large for the sizing designation (M,LXL etc). I have a 2015 Medium Aeroad and I'm 180cm which fits fine and they had an old Griepel bike on there which was also a medium, and he's around 184cm I believe.
There should be plenty of adjustment in the seatpost to accommodate your leg length (Canyon also do extra long posts), but smaller frame will have a little less reach. This will mean your position on the bike is a little less aggressive and more upright, which might suit you if you're new to road bikes.
In theory you cold swap out the bike for a different size with Canyon if you're not happy BUT they have had their supply issues, so in practice this might become a pain in the @rse. I'd also do a search on here for Canyon. There are quite a few members who've been royally messed around and have vowed never to go near them again after some speculator ordering and billing balls ups. If you can actually get the bike they're great value. Mine is wonderful, but I had my share of woe before it arrived.
