I hope the industry stays at .68 cal for the time being. It turns out that any caliber other than .68 is illegal to import into Canada, and is considered a prohibited weapon. My knowledge of this stems from trying to import two Crosman 3357 revolvers into the country. They were seized by the CBSA, and I appealed it. They are now in the RCMP gun lab undergoing ballistic testing. I got the first letter stating they were seized in January...
They said 6-12 months until they make their decision, so I guess I should make another check up call.
It comes from the fact that replica firearms are illegal to own or import into Canada. Since the kinetic energy released from calibers other than .68 is significantly less (at the same velocity), they are not considered "unregulated firearms" (this is the designation of .68 cal markers in Canada), but instead considered replicas. It turns out that if they determine the 3357s to be dangerous, I can have them just as I can import a .68 cal marker, but if it is (relatively) harmless, I cannot.
Some .68 cal markers are prohibited as well, namely RAP products. The RAP68 shotgun is prohibited as the airlines and magazines are internal, and it is indistinguishable from an actual shotgun unless under close inspection.
Just my $0.02.