A quick search finds this info online:
PIXMA iP8720 Wireless Inkjet Photo Printer Features & Specs - Canon
Specifically, re: wi-fi connectivity:
"Wireless printing requires a working network with wireless 802.11b/g or n capability."
Is your network that?
I also see references to compatibility with very old Mac OS X software (Safari 4.0 - 5.0 for Mac OS X v10.5.8 - 10.6.x) for the "Easy-WebPrint EX" software.
Also, listed in OS Compatibility is this "Mac OS® X v10.6.8 - v10.9".
I don't know when this printer was released, but it seems to me to possibly be a little older and maybe built on 32-bit software.
Did you only recently move this printer from another system you had?