I work as a paramedic and ended up purchasing the SWAT 2252 boots. Couldn't be happier, I ended up wearing them every day even off work. Much more ankle support than the Magnums they replaced, though they definitely need a break in period, at least in my experience. They're also CSA approved, so that should fit your needs.
I got mine on sale from MD Charlton for $109 plus tax.
http://www.mdcharlton.ca/specials/item/783-os-boot-2252