From Ireland to America via Quebec?

My 3rd-great-grandmother, Catherine (or Kathleen) Flynn, emigrated from Ireland and eventually settled in Gorham, Coos County, New Hampshire, where she married Iram Sydney Wells about 1860.

I haven't been able to trace her arriving through Boston. Given that Gorham is on the Atlantic & St Lawrence Railroad from Montreal to Portland, Maine, and which was a conduit for French-Canadians immigrating to work in the mills of northern New Hampshire and Maine, and because many Irish fleeing the potato famine also went to Quebec and Montreal, it seems reasonable that Catherine might have initially landed in Canada, and later made her way south.

Can anyone point me to ships' lists for immigrants arriving at Montreal or Quebec?

As for crossing into the US, previous experience with other branches of my family and with my inlaws who had connections on both sides of the border, records at the land (train) crossings are very incomplete, so I may not be able to find her entry.