You're at a tough part, Florence.. showing that a particular James McGuire in Ireland was your James McGuire in PEI. I was often lucky: My Irish ancestors that settled in Quebec and married in Quebec would have detailed marriage records that made reference to the county in Ireland that their parents were from! So it's too bad James was already married when he arrived. I looked for evidence that he, or his wife, came over with an unmarried sibling that then married in Canada -- didn't see any such evidence (anyway, I don't know if PEI marriage records typically cited that information).
Yeah, I know there are numerous trees that show the Kilegney, Co Wexford marriage of 1827, but I suspect only because of the name matches and time fit... is that enough to be reasonably confident?? Hmm..
Another avenue that can be tried is seeing what a place like AncestryDNA shows for the 'origins' of your DNA... it might show SE Ireland (Foley DNA); although if you have other ancestors that came from there then it doesn't help much (although you can examine your paternal vs maternal DNA origins separately).
Fyi, I just prepared a FindaGrave memorial for James - and also submitted requests that Johanna's and son Michael's surnames in FaG be changed from McQuire to McGuire.
Bernard