This is a bit before my period of study, but I believe the key difference was the context surrounding each. The Acadians, who had been conquered in 1713, represented a French minority under British rule who lived right next to a large, French Canadian population that was nominally hostile to the British colonial possessions. The oath of loyalty which they refused to take was far more dangerous in that context - potentially they could side with New France in a future conflict.

When Quebec is given to the British in 1763, the British had effectively defeated the major French presence in North America. Though the French still owned part of the continent, there was no longer a concentrated military force. Control of North America, as part of the reason they had fought the Seven Years War in the first place, had been achieved. In that context, the refusal of Quebecois to take an oath of loyalty is a lot less frightening. Given the military and monetary investment they had poured into taking New France, and the sheer number of Canadiens in the conquered land, exportation was never considered by British authorities in 1763.

In the US historiography the Quebec Act is seen as an important precursor to their Revolution, because its various political and territorial concessions. The soft hand used in Quebec seemed unfair to the Americans suffering under "taxation without representation" and when the French were given western territories that Americans had died defending in the Seven Years War (which they call the French-Indian War), it left a bitter taste in their mouth.

In the British historiography, the Quebec is usually considered in terms of Imperial governance. How was Britain going to govern their increasingly heterogeneous Empire? It also was a means of pacifying a "foreign" population that lived in a territory that had to be controlled for the protection of Britain's much more profitable colonies to the south (America).

Here are some good books on the topic:

Revisiting 1759: The Conquest of Canada in Historical Perspective, Phillip Buckner and John G. Reid, eds., (Toronto: University of Toronto Press, 2012) and perhaps its companion (depending on what you're looking at) Remembering 1759: The Conquest of Canada in Historical Memory

Philip Lawson, The Imperial Challenge: Quebec and Britain in the Age of the American Revolution, (Montreal: McGill-Queens Press, 1989)

Geoffrey Plank, An Unsettled Conquest: The British Campaign against the Peoples of Acadia, (Philadelphia: University of Pennsylvania Press, 2001)

N.E.S. Griffiths, From Migrant to Acadian: A North American Border People 1604-1755, (Montreal: McGill-Queens University Press, 2005)

One of the main reason for the Acte de Québec was to contain the agitation in the thirteen colonies and to avoid it to spread any further. The risk was real. Some american rebels came to Montréal to propose an alliance with them.

In fact, the act did not change much in Québec. Some would argue that it only officialised what was already the reality. Even if the royal proclamation of 1763 imposed many rules, most of them were not put to practice. The amount of english immigrant coming from the american colonies was lower than expected in Canada. Because of that, the oath was not applied because the administration needed people that spoke french. Also, the seigneurial regime was still in function during the royal proclamation period.