You should paste the letters directly onto your layout, it's not necessary to have an intermediary step of putting them on their own canvas and then moving them over ... however, if you do that, you would just need to select all layers and do "copy merged" in your edit menu and paste them to your page. I don't do it that way since you lose flexibility once you've merged them together and it's a bunch of unnecessary steps. I'm all about efficiency
HTH