Honestly, it is difficult, but not impossible, to find a phone in Canada for less than $200 CAD these days and I doubt any found at that price would be considered "flagship."
Insofar as Amazon.ca is concerned, I have purchased 2 new phones through them and both were positive experiences. My experiences with Amazon.ca have been that it has a pretty good return policy and even when you buy something through a 3rd party vendor, they will make things right if a vendor has been dishonest or unethical.
You could also try
Swiftronics Canada, who sell new, open box and used phones. I purchased through them once and it was also a positive experience. Just make sure that you read their return and refund policy before purchasing through them.
I also have sold a lot of used phones through
Kijij. All of the phones I have sold were in pristine condition and a great deal for the buyers. Although it may not seem like it sometimes, there are still honest, ethical people in this world and buying a phone through your local
Kijiji market is a good option. Just make sure to meet the seller in person and put the phone through its paces before laying down the cash.
Good luck!