Frank:
I passed on commenting on your post as I am not familiar with the Canadian EC but, here in New Jersey you can replace a regular duplex receptacle with a GFI receptacle, with no issue and no permit required.
That said, IF you have two (2) circuits with a common neutral (3 wire feed) could you convert the existing single gang box to a two gang?
IF so, why not pigtail the neutral, and install two GFI receptacles?
