BofA card can be used in Paris too, even more convenient than London. Get a BofA account, use BofA card as your main ATM card and only bring Wachovia's as backup - that was how we did.
In France, BNP is the network bank of BofA global ATM network. BNP is EVERYWHERE all over Paris.
Here is a link for where their machines are:
https://www.secure.bnpparibas.net/banque/portail/particulier/Fiche?type=fiche&identifiant=Categorie_Region_20021219163230
you can find Paris at the 2nd half of the page, and click it. That would bring you to a Paris Map and you can see BNP is EVERYWHERE.
0 fee using BofA ATM card to get Euro from BNP machines.
Our hotel was IC Le Grand, just accross street from L'Opera and there is a BNP branch right in front of L'Opera on the other side of the square. There are TWO more BNPs on Avenue de L'Opera, may be 50 yds away.
Since you are going to be in Paris for 3 weeks, you may want to consider buying the weekly transportation pass called Carte Orange - you need a 1x1 photo for that, and get it at any window of Metro or RER. It is good from Monday to Sunday, go by Zone 1-2 thru Zone 1-5, I think. CDG is zone 5 for example. Most tourist attractions in Paris are in Zone 1 or 2. Each Thursday they stop selling the same week and start selling the next week. However, the validity starts from Monday of each week. This is the stuff the Parisians use, about 50% cheaper than the pass sold to tourists. The thing comes in a card where you paste your 1x1 photo, and a ticket (billet). The ticket is good thru the week on all 3 transportation modes - Bus, Metro, and RER. Get a detail map at the same time you buy your Carte Orange - the map will become very useful when you plan your transportation from Point A to Point B.
http://www.ratp.info/informer/tarif_abonnements_o.php
No need to get Museum Pass - you would not be able to utilize it to the full value as the timeframe is too short - we visited 3 museums in our Sept trip - we went on 3 separate days, and paid as we went. It costed us a total of 24 euro per person (Cluny, Orsay and Louvre). A 2-day pass would cost you 30 euro.
Except at Orsay where we spent about 30min queing mainly due to they delayed opening (10am instead of 930am), we did not have to que at all at Louvre, and Cluny. You can get in and out Louvre during the day just to show your ticket. No line, not even at the Pyramid.
In London, the best way to pay for transportation, imo, is Oyster Card. In my post earlier you can find the Oyster Card explanation and London transportation on the TfF (Transportation for London) site.