We have a 1969 Fuse box, using 12 gauge copper wire, 100 amp service.

Long story short We were told by our home insurance and home inspection
people that in Ontario (Canada), there are no concerns with inspected copper
wired fuse boxes until they reach 50 years. So we are not rushing to
replace this box. However I wanted to install GFI receptacles for outside,
kitchen, and two bathrooms. There are none in place now. We also have a
240 volt outside outlet to run a pool motor.

Can GFI work on fuse boxes/panels? if so, does that GFI outlet, when
tripped, mean replacing the fuse? Do all the GFI's have to be on the same
circuit?

Anyone have any advice on this matter?