Rectangular tool help

I have 2 monitors with my computer, and in order to display 2 separate images as wallpaper (one image on one and another on the other, you need to make one large image with the 2 different pictures)

My 2 monitors are 2 different resolutions, so I place a 1440x900 image beside a 1280x1024 which creates a 2720x1024 image.

I like to change the pic monthly, so I usually find a picture which is not the correct resolution, so I need to resize it , and sometimes crop part of it.

So my question is can I use the rectangular marquee tool, or another tool to create a 1440x900 box that I can paste the picture of usually 1080p res into, then move it around inside the box and resize etc, then do the same for the 1280x1024 side?

when you use the Marquee tool, on the toolbar you'll see a drop-down list called "Style" that usual defaults to "Normal". if you set it to "Fixed Size" you can set the height and width ~ you can then move that over your image and crop as appropriate.