In Saskatchewan we have the regular/collector plates that support up to 7 letters. Then we also have specialty plates that only support 4 letters along with the specialty, for example Rider plates would be Rxxxx, veteran plates are Vxxxx, etc. I use the regular plates for my cars (HEMICAT, ZEE 06 and KCOBRA).
We can mix letters and numbers here in Alberta as well but we can only have 7.