Haven't eaten there myself (I'm the only one in the house who'll touch choucroute) but I know that there are a few brasseries close to Gare du Nord that specialize in choucroute. Terminus du Nord comes to mind right away, but I think there are a couple others, too.
L'Alsaco is one of a few that is not a part of a restaurant chain. Several varieties of choucroute are offered. It's more of a wine bar than brasserie, so if you want the whole Germanic touch, the Flo or Freres Blanc groups will have to do.
I don't know about others in the Flo chain, but Bofinger has a discounted takeout option that makes it a real bargain. The choucroute there is very good (if not the ultimate, whatever that is), the portion gigantic.
I do recall seeing locals eating pigs feet (?) & choucroute at Bofinger, and indeed, the portions were huge. Grace3, does Florimond always offer choucroute on the menu? If they do, that would be a good choice as well. Their other dishes are superb, IMO.
while not as refined as other options, the choucroute at Brasserie St. Louis en L'Ille is not bad.... I think the one at Bofinger was a bit more genteel (warming candle under the sauerkraut, a nice touch...etc.) but I think I prefer the slightly messier version on the Ille.