Ta Jim - whilst your quite right about that, there was no intent at presenting any of the lyric in any correct form of spelling - Scots or American - merely an attempt to put it down in a manner that read reasonably well.
'Nae' is pronounced 'nay' in many regions here in the UK - as in the expression 'nae (nay) bother' - meaning 'no problem'.
To write it out as ...
'You cannae shove your grannie aff a bus' ('aff' being 'off') may have some parts of the globe reading it wrong... as
'You cannay shove yer grannee' - even though you, me and soooo many others know 'cannae' sounds as 'canny'.
So, by writing it out as...
'You canny shove yer granny' - (or if you like, it could've been put as ..'you cannie shove yer grannie' -
the indication is therefore given that the word endings should sound the same resulting in it being pronounced (I hope) correctly by one and all, wherever they may be.
D'ye ken whit ah mean mon? Hugs - HFA