Baker Creek sells them. And they ship to Canada (free).

www.richters.com https://www.gardenate.com/plant/Luffa?zone=59 according to this site you can grow luffa gourds in Canada. https://www.agrohaitai.com/fruit&gourd/luffa/luffa.htm another Canadian firm which supplies many of the sites . Most US companies like West Coast, Baker Creek, Pinetree, Trueleaf market, etc. sell some variety of Luffa gourd.

Be aware that, formally, loofah is a tropical plant. I think it's feasible in much of the U.S., but may be harder further north. Also, I believe that the right seed is important. It is said that much of the seed that is sold produces small fruits with weak fibers. Not commercial quality. I've read that it's best to plant a bunch, and save seed from the plants that produce most successfully.

And tomatoes are also tropical in origin :-) Yet they are now cultivated pretty much globally. Loofahs are no more difficult to grow than any other cucurbit. In fact, they (and most other gourds) are quite similar to growing a winter squash. But they do need a long growing season so in more northerly locations, it's best to start indoors about 6-8 weeks before soil and air temps are sufficiently warm. About the same time you would put out tomato starts.

Full sun, rich soil, plenty of water and a strong trellis.....the vines can get very big!!

Yes, and it should go without saying that loofahs are completely frost intolerant. Unlike tomatoes and cukes, which are also frost-intolerant, the fruits take a lot of time to completely mature. I think we're talking two to three months AFTER fruit formation if you're going for a sponge. If you're just going to eat them, which you do when they are immature, time isn't an issue.

You can order cucurbita maxima seeds from West Coast Seeds in BC. Website is www.westcoastseeds.com. Some Ontario nurseries carry West Coast Seeds but they make not carry this one specifically.

What I said about saving seeds from productive plants is only a smart strategy if the plant isn't a hybrid. I believe that many of the seeds that are sold are hybrids. Many vendors don't say.

OSC also sells the seeds. That is where I got mine this year and I have 4 fruit growing. They do need full sun. I am in Zone 5b in Ontario. if you are farther north it may be hard though. I started the seeds in Jan, but I plan to start next years in December