Canary M-500 Monos- which 300B tube-

Bopper,
I've used all three of the tubes you listed in my amplifier but have no experience with your Canary. The EML XLS and the Sophia RP are much superior to the EH 300b in my SET amplifier.The EH could be a better match in your particular push pull amplifier than it was with mine. The EH is also much less expensive and you'll need 4 pairs for your mono blocks.
Charles,

Bopper,
Keep in mind that EML makes a standard 300b, a mesh plate 300b and the XLS version 300b. I haven't heard the standard 300b but I understand that it is very good. I can personally vouch for the Mesh and XLS versions. The EML aren't inexpensive but their performance justifies the higher cost. The standard EML 300b could possibly be the best value of their choices when multiple pairs are needed as in your case.
Charles,

Cfchew makes a good point, the preference for a given tube will vary with a particular amplifier. My Frankenstein SET sounds better with the EML compared to the non Royal Princess Sophia tubes, no comparison. This apparently is not the case with the Canary(different topology, circuit etc.).
Charles,