You don't need a for sale sign to sell something.
How does someone know something is for sale unless you tell them it is? Sure some people will just ask but most won't. To really succeed in online sales you must work on the presumption that everyone knows nothing so make it blatantly obvious.
I do not like the "for sale" approach because it might be an opening for someone to contest ownership with CIRA unless its a 100% pure generic.
That's why you write - "this domain
may be for sale."
I believe there is little difference between the two methods. What they do seem to have in common is that offers are usually not serious or adequate...not even to reseller levels. I believe the best results come from those who visit the whois to find your contact details.
There is a huge difference! For one you have barely one line to advertise your name with a parked page whereas with a created page you can write whatever sales pitch you want.
And what about those who choose to protect their WHOIS details? Domainers may know how to contact a .ca owner via CIRA's backward contact method but 95% of the average consumers have no clue about WHOIS let alone what to do after seeing no contact details after conducting a WHOIS search on a protected .ca!
The advantages of even a simple page far outweigh a parked page for sales imo. First a parked page is highly unlikely to be indexed by the search engines whereas a sales page/placeholder page/minisite is indexed and far more likely to bring in potential buyer's eyes to your domain.
Another advantage is better monetization until sale. Heck you might start making more than you thought and end up not wanting to sell it and instead develop it further! I do this all the time. I put up a placeholder or small website and wait and see what happens. Some do nothing but others far exceed expected traffic levels, and those get extra attention.
The fact that a domain is indexed, has backlinks, search history etc is in itself another selling feature not usually found in a parked domain. To those who develop, these things add value to a domain name.