Thank you. So how do I proof I have the PR app filed if it's not been approved yet?
Did you mean I can apply my visa extend online?
And what happens next once my PR app is approved? What happens to my visitor status? Do I have to do something?
Each case varies, and you can find a lot of comments in this forum. The bottom line is it is up to CBSA to let you in or not. It's been said some people have no problems holding a 1-way ticket is fine.
My own opinion is that having a 2-way ticket is a very strong sign to CBSA that you understand dual-intent, and importantly that your intention is not to stay and understand that you are a visitor. That you intend to leave within a period of time (by definition, that's what a visitor is). You can of course explain that your plans are not fixed which is why you have a 1-way ticket, and that you will buy a ticket from Canada. Again, it's up to the CBSA officer.
If you have not bought the ticket yet, why not buy 2-way? First of all, it's cheaper than a 1-way. If you end up not using it, just cancel the trip and let the ticket lapse. Honestly, it just raises one less question.
When you come in, you say you are visiting, that you have PR application in process. Reason why you are visiting is that your family is moving back first to prepare eventual unification of everyone, and you just want to have a few months to be with the family during this time, and return to HK in 5-6 months to prepare your own move. This also shows CBSA that you have a reason to return to HK, and not stay (again, definition of a visitor, one who enters and leaves).
Then, as with things in life, plans change, so you need to extend beyond 6 months, and so you need to extend visitor status. That's fine. The key is that you want to get in the door, and the more reasons you give the CBSA to suspect that you do not intend to leave, the more problem you may have. Unless you get a nice CBSA officer who gives you more than 6 months (some US posters here say that CBSA gave them 12 months right away) because you are waiting for your PR, don't count on the officer to be nice. The dual-intent is a very delicate thing, and very easy to slip off that delicate balance if your words do not come out the way you intended.
When you enter as a visitor, unless it states explicitly a validity, the normal entry is 6 months. You usually get a stamp. Others in the forum have said that about 1 month before the 6 months is up, you submit an application which can be done online to extend that visitor status. During the time your application is being processed, even if it goes beyond your 6 months, you are still in status until the application is concluded.
Oh, if you are in Canada when your PR is approved, meaning you get COPR, you are not PR yet. Meaning you are still visitor...so don't let your visitor status expire.
You just drive down to the US border and turn around to land. What people call flagpole.
Good luck.