Your 265W cannot use gmap3d.img so don't bother with it. You could put all of NA on an SD card in a root folder named Garmin. You can have 2 maps in there, named gmapsupp.img and gmapsup1.img. Pietu in Post #2 has separate images for Lower 49 and Canada with US Border States. Good advice from catymag, you can also do a single *.img file for just US & CA from a gmap folder using Mapsource or BaseCamp/MapInstall but maybe easier for you to use the 2 ready-made images in the SD.
As well as looking at [Only registered and activated users can see links. ] as Caty said, you can see lots more here: [Only registered and activated users can see links. ].