The only way to be certain is to buy RAM from a supplier who guarantees it for your Mac - simple as that. It will probably work (presuming you've checked the specs for your Mac and it matches up), but not certainly.
i'd email them and ask. We don't have CanadaRAM here any more to provide authoritative answers on this subject. They one you're looking at also says PC5300 as opposed to PC2-5300 - i have no idea what difference this makes if any...
Sometimes it's just less heartache to go with a supplier that guarantees it, even if you pay a little more. I'm sure CanadaRAM said something somewhere that there are subtle differences even within manufacturers, which is why Crucial frinstance, sells Mac guaranteed RAM and non-Mac guaranteed.
I've used second-hand generic brand PC RAM in the past and not had problems (that i'm aware of at least) with it in G3s, but maybe i'm just a tin-arse.