Actually most Cajuns were Acadians, expelled from the the English colonies of Nova Scotia and New Brunswick (then Acadia) to the French colony of Louisiana when the British feared that the French speaking population as a threat during the Seven-Year's War (aka the French and Indian Wars).
They pretty much ethnically cleansed Nova Scotia and PEI but many French speakers remained in New Brunswick, now Canada's only officially bilingual province. Some French speaking New Brunswickers hold a grudge even today...
Cajun is a corruption of Acadian.
http://en.wikipedia.org/wiki/Acadians
As part of the general peace in 1763 or so France gave up all claims to Quebec which later became the colony of Lower Canada and the English Parliament granted French equal status with English there.