wk989 I'm a big fan of the Park Hyatt Saigon...Especially the Terrace Rooms/Suites on the Pool floor. And especially with upgrades at booking with Prive. Great value. Breakfast is solid, though, it can feel a bit corporate at times.
As others said, Sofitel Metropole in Hanoi.
Not saying either will blow you away or anything but do think those are the best in their respective market.
Just make sure you get to Amanoi at some point of that trip
Enjoy!