Recomendar cámara y objetivo

It's not the camera, it's always the photographer. This said, if you know the limits of your camera, you will take nice pictures for stock, but effectively:

• keep the ISO low,
• stay in all manual mode,
• get the focus right,
• use a tripod.

If you want upgrading, upgrade the lens. I agree with @Jill_C, if you want to upgrade at a decent price, invest in used equipment. With cameras, check the number of releases and the sensor for dust and dead pixels. With lenses, check the glass for scratches and try the rings and the motor.  You will find good used L (with the red ring) lenses from Canon. Buy from a reliable source and let you try the lens beforehand. If you can, try to get prime lenses, especially if you are photographing staged situations. I'm only photographing with quality prime lenses. Compared to zoom lenses, prim lenses are sharper. There is one nice Canon prime lens, new for $100 (pancake 50 mm, f1.8). It's softer than my $1000 Sigma Art lens, but I've taken pleasant pictures with that lens. The disadvantage is that focussing is a bit slow.

If you want to change the system (Canon to Nikon as an example) consider that you'll have a learning curve for the new camera's haptic. But at the end, they are all great cameras. My choice at the time was Canon and as soon I had invested in lenses, I was locked in. My next choice will be mirrorless. If I can't take over my lenses, I'm not bound to a system.

That camera and lens, though rather old technology, is capable of creating good images under good lighting conditions. Are you shooting in RAW? Are you using a tripod? Are you shooting in Manual mode and selecting the correct shutter speed, aperture and ISO? Do you understand the basics of composition? Are you proficient at editing in Lightroom or Photoshop? Those older Canon Crop sensor DSLR's do not do well with high ISO and create very noisy images. Once you have learned how to fully utilize the features of that camera, you should consider an upgrade. I can't really advise what you to buy because I don't know what you consider a "reasonable price". Newer versions of the Canon crop sensor models offer improved performance. You can also consider upgrading to a full frame sensor DSLR. Many photographers are selling their used DSLR gear as they upgrade to the mirrorless  platform.