Concerning the locations - firstly in the "Groves of Boho" as posted by Mary Conway and closely similar to that in the versions in "Hidden Fermanagh" (supplied by Cathal McConnell) -

Sillees - River and also forest flowing as I stated above though Moss Lough should indeed be Ross Lough as was noted by the anonymous guest immediately above.
Monea - close to Lough Erne shore a few miles to the SE of Derrygonnelly
Stratore - to the SW of Derrygonnelly
Carngreen, also known as Carn - just west of Boho.
Knockmore - a townland near Derrygonnelly.

In other words, all those given can be located around or close to Boho.

Turning to Séamus (or as his book gives it 'Seumas') MacManus' "The little linnet of Boe"

Murlo - does not exist in Ireland unless as Murlough of which there are several ranging from County Down to NE Antrim - there is such a place in Tuscany!
Sthragar - does not exist - perhaps a misspelling of Strathgar though the nearest of this name is in Scotland.
Caroo - not local, the nearest use of the name is in Kinawley across Fermanagh.
Glenvar - not in Fermanagh, there are such places in Donegal and Tyrone.

I find it hard to accept that the traditional versions would have altered these, mainly fictitious place-names to local ones, at least not as convincingly. However, the version given by Cathal McConnell contains(Verse 5 line 3) "Farewell I'll cry, I'll weep and sigh for me now guile and woe" which compares with MacManus' "Farewell, I'll cry and wave my hand; 'Farewell to gilded woe'" and it's hard to see other than that McConnell derives from MacManus. Also, the spelling 'leverock', more commonly 'laverock' in 'Hidden Fermanagh' is the same as MacManus. The verse order in MacManus is more logically ordered, the story has a real sequence.

All in all, without other evidence, it seems more likely that MacManus was the author and that his poem was adapted/adopted traditionally. I can't see anywhere else where he might have adapted a traditional song.

Séamus MacManus' book can be downloaded and saved as a pdf and individual pages can be printed at that stage. Alternatively, single pages can be copies and pasted into a word processing document and printed from that.