Most large US & Canadian resorts have XC trails, of varying quality, attached. I have enjoyed jaunts at Jackson Hole, Telluride, Big White and (gasp) Sun Peaks (not particularly flat). There are also numerous XC only setups.https://www.ski.com/blog/14-u-s-ski-resorts-with-awesome-cross-country-skiing/
Lake Placid looks quite good and I have a girlfriend in NYC. Is Lake Placid any good for XC skiing? It looks COLD!.