You will need to use #3(i beleive that is the same in USA as Canada) .
If this was my install I would put a short piece of EMT in between the sub and the main. You probably would have to take the sub off the wall to do this but that doesn't look like it would be to hard. This will give you a nice clean install.
You could also use NMD90 or AC90 in between the two panels.
If this was my install I would put a short piece of EMT in between the sub and the main. You probably would have to take the sub off the wall to do this but that doesn't look like it would be to hard. This will give you a nice clean install.
You could also use NMD90 or AC90 in between the two panels.