I'm pretty sure the basic comcept behind them is the same, but the higher the Category is, the better quality the cable is i.e. it can transfer at higher frequency/speeds, or go longer distances at lower speeds without losing signal. Where'd you find CAT7? I didn't find any CAT7's in Canada.... I'd suggest you go with the CAT7 if you want to future-proof your network for faster speeds like 10G, unless you're happy with 1G.
Cat7 is for long-distance networks. Cat6A is the highest "normal" ethernet standard, created specifically for 10GBaseT networking: 10Gigabit copper ethernet. Right now everything is gigabit, but 10 gigabit is coming soon, right now only a few server adapters, but 10GBaseT might be standard on new motherboards in a year or two.
Cat5 - official for 100Mbps - works on gigabit for small distances
Cat5e - verified working for gigabit on small distances
Cat6 - official gigabit cabling
Cat6A - official 10GBaseT cabling
Cat7 - long distance (dunno if 10GBaseT works on Cat7 - it should)