For early Irish emigration to Upper or Lower Canada, it's worth checking the McCabe List. This is an 1829 petition to the Crown, signed by about 700 Irishmen, many of them canal labourers, in the Bytown [now Ottawa] area, asking for relief for their relations back in Ireland. Basically, they wanted the government to help pay the passage of their relatives to Canada and give them some land. Many of the petitioners named their parishes and counties of origin. They also tended to name a local magistrate or clergyman back home who could vouch for them (note: in some cases the petitioner is RC, but names a Protestant clergyman as reference).
So I just checked it for you, and there are several McGuires on this petition:
Francis McGuire (McCabe List #587), signed (or rather, marked with his X), and said he was from Nockbride in Cavan, and reported: "Has an uncle, James McGuire, with a family residing at Nock bridge in the Co. of Cavan, for whom he is desirous of obtaining land."
John McGuire (McCabe List #360) signed (marked with X) and said he was from Nockbride in Cavan. "has a cousin Phillip Cusick, with his family reside at Baly Burn in Parish of Nockbride and is known to the Revd Mr Baily of Said place."
Peter McGuire (McCabe List #222) signed, and said he was Mountbride in Cavan. "This applicant's father, Dennis McGuire, with a large family reside in Mountbride in the County Cavan he is known to the Revd Samuel Adams."
There is also a John McGuire from Kildare (ML#389) and a James McGuire from Donegal (ML#640).
For early Irish emigration to Ontario/Quebec, you should also check Al Lewis's Bytown or Bust site. Many Irish originally went to Bytown, before moving on to help settle other parts of Canada (and the US).
