Just to close the loop, last followup.
They never replied to my request to cancel my order.
Finally, 13 days after I placed the order, they informed me one of my "in stock, ships in 2-3 days items" would not be available so they were going to refund me that amount and ship the rest that day. Despite my request to cancel.
So I asked again to cancel the whole order as originally requested.
They refunded me $3.75 for one small item, not the whole order amount.
I went back and forth with CS several times, with screenshots from PayPal showing in my account the refunded amount is clearly less than the order amount.
The reply I got? "I have checked the Niagara Cycle account again this morning and I assure you that you have been refunded the entire amount of your order. "
These people are either criminals or criminally incompetent. I've never seen a business this badly run, and whether or not they intend to rip people off, it was clear to me as my order extended into week 2 that they must receive a not-insignificant chunk of their revenue from people who simply give up trying to deal with them. At the end of the day it doesn't much matter to me if they intend to rip people off, because they clearly end up dealing dishonestly in one way or another.
PayPal dispute filed; lesson learned to always use a credit card. 99.9% of the time I do, but this time... whoops, my bad.