Speaker regularly can't split two alternatives (6)
I believe the answer is:
orator
'speaker' is the definition.
(orator is a kind of speaker)
'regularly can't split two alternatives' is the wordplay.
'two alternatives' can mean two replacements for 'alternative'.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'split' indicates putting letters inside (some letters split a word into two).
'alternative' becomes 'or'.
'alternative' becomes 'or'.
The alternate letters of 'cant' are 'at'.
'or'+'or'='oror'
'at' placed inside 'oror' is 'ORATOR'.
(Other definitions for orator that I've seen before include "A Rhetorical talker or speech-maker" , "Formal speech maker" , "One addressing" , "Skilled public speaker" , "To roar at a speech-maker" .)