Did they have any and are there any still in service?
Here is a reference that should at least start answering your questions.
4803 is preserved in Toronto, in original colors, and is supposed to be reasonably complete except for traction motors. That’s the nearest thing to ‘service’ that I’d expect from a GMD GP7, although you might want to research whether any were sold to shortlines and might still be operating. I don’t think Grand Trunk had any 7s, despite the existence of models painted that way.
Now, if you had asked about GP9s, the story would be somewhat different. CN had a large number, GT had more than a few, there’s been a rebuilding program for them, and apparently quite a few of the rebuilds are still running (I think we have at least 2 operating in the Memphis area).
Yes.
No.