There hasn't been a new AR-180b come into Canada in what, two years? The only source is to scrabble around for one on the used market.
The XCR is in serious demand and very short supply. The waiting list to get one new has to be close to a year. Your only source to get one in a reasonable period of time is to scrabble around for one on the used market.
SIGs have been in steady supply for years. I can think of stores that I could walk into tomorrow and buy one off the shelf. A couple of Canada's best known mail order type places list them in stock.
The AR-180b was an attempt by an aftermarket maker to create an economy rifle for recreational use. The XCR is an attempt by an aftermarket maker to create a serious rifle, but it is an new an unproven design. SIG is a century old industrial and military firm that has made combat arms for years. The Black Special is a combination of some of their successful products.
SIG. It isn't even a question.