I've posted in a few different topics on this forum about this.
For example, Shoppers allows me to book appointments online for May 5th when I need my test. I stopped in at Shoppers the other day for my prescription and mentioned it to the pharmacist. He told me no that they wouldn't do the testing. He argued with me when I said but I can book an appointment online for this store. He said that doesn't matter, they wouldn't do the test.
As for Walmart, there are no appointments online lately. I called the Walmart pharmacy last week and the pharmacy associate I spoke to said not to worry about booking online just walk in. My husband stopped in there today and the pharmacist told him no walk ins, and to keep checking if appointments open up. He said that only select staff members will do the testing and it depends what days they work.
So I don't know if its just something about these places in my city or not but I definitely don't feel comfortable relying on them for testing at this point.