This came up a while back, and I dug into a Google Images search of various terms such as "Hand engraving firearms Canada" and came up with a larger number of potential engravers than I thought I would.
Styles and prices vary, I have not used any of them.
Of note, is that the frame, technically, is the only part that is considered to be the actual "Firearm" in the eyes of the Laws. Any other part can be left with pretty much anyone, for work (except, maybe, barrels that are below prohib length, I think, they are a prohibited device on their own) so to get the frame engraved you need to find an engraver that has firearms possession papers that will cover the class involved, IIRC.
Whether an individual engraver will take on gun work though, is up to them. But if you find them by following through from pictures of gun parts or guns, it's probably a good sign.
Cheers
Trev