Singles are flown across by pilots experienced in the crossing. Their success should not be taken as an indication that it's easily done. I've done the crossing a few times in twins, and having done it, would not consider it in a piston powered single, unless you had unlimited time to wait at each stop for the perfect conditions. Certainly, when it works, it's a great trip, but there are so many opportunities for it to go wrong. When it does, mostly the weather, there are few alternates within range. Narsarsuaq is a shorter route stop, but not much for alternates.
Most GA singles do not have the payload to carry ferry fuel in tanks, and the required emergency gear. Some can be flown overgross for ferry, so you have to research.
The emergency equipment is obtainable, but returning it following the trip can be surprisingly difficult. Shipping rafts and vests with gas cylinders is silly expensive. The last time I was involved, it was less costly to just buy the raft than ship it back to the renter, which is what was done. Depending upon the route through north east Canada, you may have to prearrange fuel, and be prepared to pump it from drums with a pump you take along - I have had to do this. And, you're buying the whole drum (very $$$) whether you use it or not.
Any maintenance you could need will be difficult to arrange at most stops along the way. Ferry fuel systems, if needed, require good design, and approval, I've approved a couple of them. There have been occasions where a ferry fuel system did not work. When this happens, you can actually be going down with cabin fuel you cannot use, the worse way to carry fuel!
And then there's the weather. A very thorough understanding of the weather systems is vital, and the willingness to sit and wait it out. One friend of mine spent eight days at a remote Greenland airport - just reading a book, while he waited.
I think occasionally groups of pilots do the crossing, and that's sure a better way, at least there is help more near...