I'm not going to quote everyone as some of this will be repeated.
Waterloo, since you don't want to move just yet you really are at the discretion of the border official. It used to be if you didn't want to endorse the visa you left the packet at home. Now with things being digital, they may not be able to catch it and it not endorse things. Like what happened with Family One.
You will also want to get that sale on the house done and settled before your move date. Once you endorse that visa for tax purposes the sale of the house becomes a pain. ( I can't help you with what all is involved, but others have regretted not having the sale finale before the move.)
As for medical yes it is gone when you endorse the visa. No they won't know if you use it right away but Canada has cracked down on this and when they put two and two together they will send you the full bill for it. That could be years later but they will.
Too many ppl confuse what snowbirds and students do to ppl who are immigrating out of Canada. One is temporary not living out of Canada the other is actually leaving Canada.
As for those who live on the border, or dual citizens again it goes by where do you hang your hat? Working in the US but living in Canada means you are a Canadian resident. I know a Canadian CBP agent who moved to the US works for the Canadian CBP and she and her kids cannot use Canadian health care. Remember any additional health insurance provided by an employer is add on insurance. It's supplemental insurance to compliment the provincial insurance.
Now if you live in one of the few provinces that you pay a small amount for your provincial insurance then things are a bit different. BC for example has you pay ahead for your insurance. SO coverage for them would last until that day they list as your coverage period.