Interesting. I had always heard it was illegal as a food substance or additive but not as a chemical and that's why it was (basically) impossible to find Mrs. Wages brand pickling lime in stores up here whereas it's pretty easy to find Stateside... the only thing that I can find at the CFIA site is a listing for Univar's calcium hydroxide in two different powdered forms but both listed as acceptable. I can't find anything online about whether it really is banned except for basically threads like this on aquaria boards but without links to back up the claim it's just hearsay. So I guess I've learned something new tonight. For like 10 years I thought you couldn't buy it (as pickling lime that is) because it wasn't allowed to be sold that way.
Nevertheless whatever the explanation, bottom line is it's still hard to find as a pickling lime, but easy to find as kalk, and our fine sponsors would be happy to sell some, so my recommendation there still stands.
Another thought is that you get what you pay for. I bought Mrs. Wages pickling lime in a group order from the U.S. by Canreefers a few years ago (before it was easy to buy in bulk from places like Bulk Reef Supply et al), and it was nice because it was moderately cheaper but the stuff was nowhere near as nice to use as real kalk. My kalk reactor water would get yellow/brown within a few days and look really gross. Whereas the BRS kalk stays white in the kalk reactor. I'm assuming it's a purity thing and for that reason alone I'd still recommend that pickling lime isn't worth the wild goose chase.
cheers