The lower point is well defined, the 366 fps bit. However, I've found the upper limit of 500 fps or 5 joules still causes trouble.
For instance, while browsing Evike I noticed they have a new Mosin Nagant M44 CO2 rifle that fires something like 570 fps. However, Evike goes simply by the 500 fps rule so it's not listed as "Canada Legal" on their site and you can't even advance through the ordering process.
I got in touch with their customer service department and they insisted the limit was 500 fps until I linked/quoted the actual memorandum that states 500 fps or 5 joules of energy part.
They then conceded a little, and said they'd have their policy people look into it. But then they went on to say that they've had Canadian customers order 500+ fps guns and had them seized by CBSA.
They also said that I could order the gun through them if I wanted, but I'd have to wire them money directly rather than purchasing through the site.