"I canna raise the win'" or as I sing it, "I canna fin' the win'" means the same thing, but put a different way. Or it could tie in with the line I mention about alternative lines I have heard, "Gie yer rigs (pipes) a bla'" which is substantially the same as, "Gie yer airs (tunes) a bla'" It's got nothing to do with witches, etc. Let's not get too fancifu. Another alternative meaning is that times are hard in Scotland and he is finding it hard to make a living.

"And a' I need's my daily fare and whit'll pey my doss. Means all he needs is enough to eat and somewhere to sleep. (doss - modern equivelant-crash)
Land end?? It's never mentioned in the song. John O' Groat's is only mentioned in the song as a place he has been, but he never gets out of Scotland. The farthest South he gets is Galloway/Stranraer in south west Scotland.

Gutcher has the right of it. :)

The tune has been ussed in a number of songs including Hatton Woods (Sheila Stewart) I pity The Poor Immigrant (Bob Dylan) amongst others.