If sticking with canon is that important, and not having to make things up is also important, then you've got a serious problem running an FR game. Because most places just don't have enough detail for you. You HAVE to make up most of the information your players demand outside a tiny number of places. Also, even if you play in one of those and the players show no interest at all in going somewhere else you will run out of adventure hooks in that location at some point, after which you have to Make Stuff Up.
Sticking to canon is not as important as having a detailed setting (did you note that I tend to ignore all RSEs, unless they fit my campaign?). Now, I could grab any Volo's Guide, for example, and run a game in most of the settings described in them. Add in the boxed sets and FR Adventures, and there's no need for "extra" details. Just to name a few such places: Scornubel, Arabel, Suzail, Elturel, Hill's Edge, Berdusk, Silverymoon -- not to mention, naturally, Waterdeep. And, whatever details I might feel are still missing to satusfy my players, I could do myself. With Volo's Guide to the North, I could have a pretty decent "Tour de North"-type of campaign, with even smaller settings detailed "well enough" (major inns, shops, NPCs, adventure locations) for me to use them with minor tweaks.
And, yes, I have to "Make Stuff Up" for each session anyway (the session's adventure, at least) -- that wasn't the point. If the players wouldn't want the level of details they do, I wouldn't *force* it on them. Also, over the years I've kind of learned how to "hook" them; no need to worry about "wasting" adventure hooks. For example, if I tried the old cliché with the "mysterious employer" at the local inn + lots of combat encounters, they wouldn't think it was a fun session. Spending half the session in role-playing with themselves and the NPCs, with adventure hooks tied to character backgrounds... now, that's their idea of fun.
Anyway, my point was, I'd have to start with a "clean slate" in 4E FR, because I could hardly expect to grab my 2E/3E accessories and use the stuff "as is". In fact, it would probably be easier to pick a small village and start from scratch, than trying to update the info and the maps.
Why did the Realms become the most popular D&D setting? It didn't. That's Homebrew Game.
By a huge margin.
I
I suspect that you realized I'm talking of D&D settings *published* by TSR/WoTC.