Looking for advice on choosing a digital SLR for landscape / night photography

Would it be better for me to ship for Nikon and leave from there or should I continue with Canon and use the few goals I already have?

You put the cart a little before the horse.

It would be best for you to stay with your camera and your current goals while you start learning photography in ernest. The EOS Rebel T3 and the commonly used lenses in no way prevent your photographic skills and technique from improving. During this process, you will discover the directions you want to take, and what you may need to move up a gear.

Although there are specific types of lenses and, to a lesser extent, cameras, for specific photographic tasks, the areas of "landscape" and "astrophotography" are quite wide. You would not necessarily want the same lens to be used for very wide-angle stellar contrasts, as for narrower deep-sky objects.

So before you wet your feet, stay with what you already have up to the point where you know what you have to do what you want to do.

For more information, please see these questions and their answers here at Photography SE:

When should I improve the case of my camera?
How to know that your equipment has become too small?
Is the camera important?
the best way to improve the sharpness of the image on the Canon 700D
Should I upgrade my Canon case or lens for a future trip?
Should I buy a new DSLR camera or spend money in a photography class with my point & shoot?