Koodo at my local branch mentioned they are in the works to get the 64, but that's the extent of the information, or even likelihood of any other storage sizes of the s6 variants Koodo will offer. Sadly so, the 64 is still out of reach for the time being.
You'll be MUCH better off with an LG G4....and it's not going to be as expensive as the S6 64GB or God forbid, the 128GB.
I am patient...will wait for G4. Replaceable battery and SD card with better camera...trumps S6. My 2 (unsolicited) cents :)