I'm from WI, not Alberta, so this might or might not help you.
I've done both AF and air and both worked equally well. I personally believe that, if I am comfortable that I have truly blown out the system leaving little water in the lines, than there is little to freeze so there is little expansion.
I have read from one of our Canadian members that they like to use both methods. That is, they flush with AF and then blow out the water lines thinking that at least any residual liquid will have some AF in it.
Good idea to plan on AF in the traps and to keep the toilet seal from drying out.
DW, 3 Kids and our Goldens
2012 Shamrock 233S
2008 Toyota Sequoia 5.7L 4WD